Cytostatic agents

ABSTRACT

Compounds of formula 1                    
     wherein R 4  is an ester or thioester group, and R, R 1 , R 2  and R 3  are as defined in the specification are inhibitors of rapidly dividing tumour cells.

The present invention relates to therapeutically active esters and thioesters, to processes for their preparation, to pharmaceutical compositions containing them, and to the use of such compounds in medicine. In particular, the compounds are inhibitors of the proliferation of a range of rapidly dividing tumour cells, for example melanoma and/or lymphoma cells.

BACKGROUND TO THE INVENTION Anti-Proliferative Agents

There is a need in cancer therapy for therapeutic compounds which are inhibitors of the proliferation of tumour cells. One compound which is known to have such activity is 5-fluorouracil (5-FU).

Anti-Metastatic and Anti-Invasive Agents

Compounds which have the property of inhibiting the action of the metalloproteinase enzymes involved in connective tissue breakdown and remodelling, such as fibroblast collagenase (Type 1), PMN-collagenase, 72 kDa-gelatinase, 92 kDa-gelatinase, stromelysin, stromelysin-2 and PUMP-1 (known as “matrix metalloproteinase”, and herein referred to as MMPs) have been proposed and are being tested in the clinic for the treatment of solid tumours. Cancer cells are particularly adept at utilising the MMPs to achieve rapid remodelling of the extracellular matrix, thereby providing space for tumour expansion and permitting metastasis. MMP inhibitors should minimise these processes and thus slow or prevent cancer progression.

A known class of MMP inhibitors having a hydroxamic acid group as the zinc binding group may be represented by the structural formula (IA)

in which the groups R₁ to R₅ are variable in accordance with the specific prior art disclosures of such compounds. Examples of patent publications disclosing MMP inhibitors of formula (IA) are:

US 4599361 (Searle) WO 93/24475 (Celltech) EP-A-2321081 (ICI) EP-A-0574758 (Roche) EP-A-0236872 (Roche) EP-A-0575844 (Roche) EP-A-0274453 (Bellon) WO 94/02446 (British Biotech) WO 90/05716 (British Biotech) WO 94/02447 (British Biotech) WO 90/05719 (British Biotech) WO 94/21612 (Otsuka) WO 91/02716 (British Biotech) WO 94/21625 (British Biotech) WO 92/09563 (Glycomed) WO 94/24140 (British Biotech) US 5183900 (Glycomed) WO 94/25434 (Celltech) US 5270326 (Glycomed) WO 94/25435 (Celltech WO 92/17460 (SB) WO 95/04033 (Celltech) EP-A-0489577 (Celltech) WO 95/04735 (Syntex) EP-A-0489579 (Celltech) WO 95/04715 (Kanebo) EP-A-0497192 (Roche) WO 95/06031 (Immunex) US 5256657 (Sterling) WO 95/09841 (British Biotech) WO 92/13831 (British Biotech) WO 95/12603 (Syntex) WO 92/22523 (Research Corp) WO 95/19956 (British Biotech) WO 93/09090 (Yamanouchi) WO 95/19957 (British Biotech) WO 93/09097 (Sankyo) WO 95/19961 (British Biotech) WO 93/20047 (British Biotech) WO 95/19965 (Glycomed) WO 93/24449 (Celltech) WO 95/22966 (Sanofi Winthrop) WO 95/23790 (SB)

BRIEF DESCRIPTION OF THE INVENTION

This invention is based on the identification of a class of ester and thioester compounds which inhibit proliferation of rapidly dividing cells. The ester and thioester compounds in question have certain structural similarities to known MMP inhibitors of general formula (IA) above disclosed in the foregoing patent publications. How ever, instead of the amide group —CONR₄R₅ of formula (IA), they have an ester or thioester group. Despite the similarity of structure, it has been shown that compounds of the invention which have little or no MMP inhibitory activity are nonetheless potent inhibitors of such cell proliferation, implying a novel mechanism is at work. This antiproliferation property suggests a utility for the compounds of the present invention in the treatment of cancers.

Although the patent publications listed above predominantly disclose MMP inhibiting compounds of formula (IA), ie having an amide group —CONR₄R₅, a few (WO 92/09563, U.S. Pat. No. 5,183,900, U.S. Pat. No. 5,270,326, EP-A-0489577, EP-A-0489579, WO 93/09097, WO 93/24449, WO 94/25434, WO 94/25435, WO 95/04033, WO 95/19965, and WO 95/22966) include within their generic disclosure compounds having a carboxylate ester group in place of the amide group. The carboxylate ester compounds with which this invention is concerned thus represent a selection of a notional subclass from the compounds proposed in the art as MMP inhibitors, for a specific and previously unrecognised pharmaceutical utility.

WO 95/04033 discloses N⁴-hydroxy-N¹-(1-(S)-methoxycarbonyl-2,2-dimethylpropyl)-2-(R)-(4-chlorophenylpropyl)succinamide as an intermediate for the preparation of the corresponding methylamide MMP inhibitor. In addition, Int. J. Pept. Protein Res. (1996), 48(2), 148-155 discloses the compound

Ph—CH₂CH(CO-Ile-OtBu)CH₂CONHOH

as an intermediate in the preparation of compounds which are inhibitors of neurotensin-degrading enzymes. However, those two appear to be the only specific known carboxylate ester compounds of the kind with which this invention is concerned.

The present inventors' findings of inhibition of proliferation of rapidly dividing cells, including such tumour cells as lymphoma, leukemia, myeloma adenocarcinoma, carcinoma, mesothelioma, teratocarcinoma, choriocarcinoma, small cell carcinoma, large cell carcinoma, melanoma, retinoblastoma, fibrosarcoma, leiomyosarcoma or endothelioma cells, by the esters and thioesters of the present invention, by a mechanism other than MMP inhibition, is not disclosed in or predictable from those earlier publications.

DETAILED DESCRIPTION OF THE INVENTION

In its broadest aspect, the present invention provides a method for inhibiting proliferation of tumour cells in mammals, comprising administering to the mammal suffering such proliferation an amount of a compound of general formula (I) or a pharmaceutically acceptable salt hydrate or solvate thereof sufficient to inhibit such proliferation:

wherein

R is hydrogen or (C₁-C₆)alkyl;

R₁ is hydrogen;

(C₁-C₆)alkyl;

(C₂-C₆)alkenyl;

phenyl or substituted phenyl;

phenyl (C₁-C₆)alkyl or substituted phenyl(C₁-C₆)alkyl;

phenyl (C₂-C₆)alkenyl or substituted phenyl(C₂-C₆)alkenyl

heterocyclyl or substituted heterocyclyl;

heterocyclyl(C₁-C₆)alkyl or substituted heterocyclyl(C₁-C₆)alkyl;

a group BSO_(n)A— wherein n is 0, 1 or 2 and B is hydrogen or a (C₁-C₆) alkyl, phenyl, substituted phenyl, heterocyclyl substituted heterocyclyl, (C₁-C₆)acyl, phenacyl or substituted phenacyl group, and A represents (C₁-C₆)alkylene;

hydroxy or (C₁-C₆)alkoxy;

amino, protected amino, acylamino, (C₁-C₆)alkylamino or di-(C₁-C₆)alkylamino;

mercapto or (C₁-C₆)alkylthio;

amino(C₁-C₆)alkyl, (C₁-C₆)alkylamino(C₁-C₆)alkyl, di(C₁-C₆)alkylamino(C₁-C₆)alkyl, hydroxy(C₁-C₆)alkyl, mercapto(C₁-C₆)alkyl or carboxy(C₁-C₆)alkyl wherein the amino-, hydroxy-, mercapto- or carboxyl-group are optionally protected or the carboxyl-group amidated;

lower alkyl substituted by carbamoyl, mono(lower alkyl)carbamoyl, di(lower alkyl)carbamoyl, di(lower alkyl)amino, or carboxy-lower alkanoylamino; or

a cycloalkyl, cycloalkenyl or non-aromatic heterocyclic ring containing up to 3

heteroatoms, any of which may be (i) substituted by one or more substituents selected from C₁-C₆ alkyl, C₂-C₆ alkenyl, halo, cyano (—CN), —CO₂H, —CO₂R, —CONH₂, —CONHR, —CON(R)₂, —OH, —OR, oxo-, —SH, —SR, —NHCOR, and —NHCO₂R wherein R is C₁-C₆ alkyl or benzyl and/or (ii) fused to a cycloalkyl or heterocyclic ring;

R₂ is a C₁-C₁₂ alkyl,

C₂-C₁₂ alkenyl,

C₂-C₁₂ alkynyl,

phenyl(C₁-C₆ alkyl)-,

heteroaryl(C₁-C₆ alkyl)-,

phenyl(C₂-C₆ alkenyl)-,

heteroaryl(C₂-C₆ alkenyl)-,

phenyl(C₂-C₆ alkynyl)-,

heteroaryl(C₂-C₆ alkynyl)-,

cycloalkyl(C₁-C₆ alkyl)-,

cycloalkyl(C₂-C₆ alkenyl)-,

cycloalkyl(C₂-C₆ alkynyl)-,

cycloalkenyl(C₁-C₆ alkyl)-,

cycloalkenyl(C₂-C₆ alkenyl)-,

cycloalkenyl(C₂-C₆ alkynyl)-,

phenyl(C₁-C₆ alkyl)O(C₁-C₆ alkyl)-, or

heteroaryl(C₁-C₆ alkyl)O(C₁-C₆ alkyl)- group,

any one of which may be optionally substituted by

C₁-C₆ alkyl,

C₁-C₆ alkoxy,

halo,

cyano (—CN),

phenyl, or

phenyl substituted by

C₁-C₆ alkyl,

C₁-C₆ alkoxy,

halo, or

cyano (—CN); p1 R₃ is the characterising group of a natural or non-natural α amino acid in which any functional groups may be protected; and

R₄ is an ester or thioester group,

or a pharmaceutically acceptable salt, hydrate or solvate thereof.

In another broad aspect of the invention, there is provided the use of a compound of formula (I) as defined in the immediately preceding paragraph, in the preparation of a pharmaceutical composition for inhibiting proliferation of tumour cells in mammals.

The present invention also provides novel compounds of general formula (I) above wherein R, R₁, R₂, R₃ and R₄ are as defined above with reference to formula (I), and pharmaceutically acceptable salts, hydrates or solvates thereof, PROVIDED THAT:

(i) when R and R₁ are hydrogen, R₂ is 4-chlorophenylpropyl, and R³ is tert-butyl, then R₄ is not a methyl carboxylate ester group; and

(ii) when R and R₁ are hydrogen, R₂ is phenylmethyl, and R³is 1-methylprop-1-yl, then R₄ is not a tert-butyl carboxylate ester group.

One particular sub-group of the novel esters and thioesters of the invention consists of compounds of formula (I) above, wherein:

R, R₁ and R₄ are as defined above with reference to formula (I)

R₂ is C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl,

biphenyl(C₁-C₆ alkyl)-, phenylheteroaryl(C₁-C₆ alkyl)-, heteroarylphenyl(C₁-C₆ alkyl)-,

biphenyl(C₂-C₆ alkenyl)-, phenylheteroaryl(C₂-C₆ alkenyl)-, heteroarylphenyl(C₂-C₆ alkenyl)-,

phenyl(C₂-C₆ alkynyl)-, heteroaryl(C₂-C₆ alkynyl)-,

biphenyl(C₂-C₆ alkynyl)-, phenylheteroaryl(C₂-C₆ alkynyl)-, heteroarylphenyl(C₂-C₆ alkynyl)-,

phenyl(C₁-C₆ alkyl)O(C₁-C₆ alkyl)-, or heteroaryl(C₁-C₆ alkyl)O(C₁-C₆ alkyl)-,

any one of which may be optionally substituted on a ring carbon atom by C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, or cyano (—CN); and

R₃ is C₁-C₆ alkyl, optionally substituted benzyl, optionally substituted phenyl, optionally substituted heteroaryl; or

the characterising group of a natural α amino acid, in which any functional group may be protected, any amino group may be acylated and any carboxyl group present may be amidated; or

a heterocyclic(C₁-C₆)alkyl group, optionally substituted in the heterocyclic ring;

and pharmaceutically acceptable salts, hydrates or solvates thereof.

As used herein the term “(C₁-C₆)alkyl” or “lower alkyl” means a straight or branched chain alkyl moiety having from 1 to 6 carbon atoms, including for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, n-pentyl and n-hexyl.

The term “(C₂-C₆)alkenyl” means a straight or branched chain alkenyl moiety having from 2 to 6 carbon atoms having at least one double bond of either E or Z stereochemistry where applicable. This term would include, for example, vinyl, allyl, 1- and 2-butenyl and 2-methyl-2-propenyl.

The term “C₂-C₆ alkynyl” refers to straight chain or branched chain hydrocarbon groups having from two to six carbon atoms and having in addition one triple bond. This term would include for example, ethynyl, 1-propynyl, 1- and 2-butynyl, 2-methyl-2-propynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl and 5-hexynyl.

The term “cycloalkyl” means a saturated alicyclic moiety having from 3-8 carbon atoms and includes, for example, cyclohexyl, cyclooctyl, cycloheptyl, cyclopentyl, cyclobutyl and cyclopropyl.

The term “cycloalkenyl” means an unsaturated alicyclic moiety having from 4-8 carbon atoms and includes, for example, cyclohexenyl, cyclooctenyl, cycloheptenyl, cyclopentenyl, and cyclobutenyl. In the case of cycloalkenyl rings of from 5-8 carbon atoms, the ring may contain more than one double bond.

The term “aryl” means an unsaturated aromatic carbocyclic group which is moncyclic (eg phenyl) or polycyclic (eg naphthyl).

The unqualified term “heterocyclyl” or “heterocyclic” means (i) a 5-7 membered heterocyclic ring containing one or more heteroatoms selected from S, N and O, and optionally fused to a benzene ring, including for example, pyrrolyl, furyl, thienyl, piperidinyl, imidazolyl, oxazolyl, thiazolyl, thiadiazolyl, pyrazolyl, pyridinyl, pyrrolidinyl, pyrimidinyl, morpholinyl, piperazinyl, indolyl, benzimidazolyl, maleimido, succinimido, phthalimido, 1,2-dimethyl-3,5-dioxo-1,2,4-triazolidin-4-yl, 3,4,4-trimethyl-2,5-dioxo-1-imidazolidinyl, 2-methyl-3,5-dioxo-1,2,4-oxadiazol-4-yl, 3-methyl-2,4,5-trioxo-1-imidazolidinyl, 2,5-dioxo-3-phenyl-1-imidazolidinyl, 2-oxo-1-pyrrolidinyl, 2,5-dioxo-1-pyrrolidinyl or 2,6-dioxopiperidinyl, or (ii) a naphththalimido (ie 1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl), 1,3-dihydro-1-oxo-2H-benz[f]isoindol-2-yl, 1,3-dihydro-1,3-dioxo-2H-pyrrolo[3,4-b]quinolin-2-yl, or 2,3-dihydro-1,3-dioxo-1H-benz[d,e]isoquinolin-2-yl group.

The term “heteroaryl” means a 5-7 membered substituted or unsubstituted aromatic heterocycle containing one or more heteroatoms. Illustrative of such rings are thienyl, furyl, pyrrolyl, imidazolyl, thiazolyl, pyrazolyl, isoxazolyl, isothiazolyl, trizolyl, thiadiazolyl, oxadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl and triazinyl.

The term “ester” or “esterified carboxyl group” means a group R₉O(C═O)— in which R₉ is the group characterising the ester, notionally derived from the alcohol R₅OH.

The term “thioester” means a group R₉S(C═O)— or R₉S(C═S)— or R₉O(C═S)— in which R₉ is the group characterising the thioester, notionally derived from the alcohol R₉OH or the thioalcohol R₉SH.

Unless otherwise specified in the context in which it occurs, the term “substituted” as applied to any moiety herein means substituted with up to four substituents, each of which independently may be (C₁-C₆)alkyl, (C₁-C₆)alkoxy, hydroxy, mercapto, (C₁-C₆)alkylthio, amino, halo (including fluoro, chloro, bromo and iodo), nitro, trifluoromethyl, —COOH, —CONH₂, —CN, —COOR^(A), —CONHR^(A) or —CONHR^(A)R^(A) wherein R^(A) is a (C₁-C₆)alkyl group or the residue of a natural alpha-amino acid.

The term “side chain of a natural or non-natural alpha-amino acid” means the group R¹ in a natural or non-natural amino acid of formula NH₂—CH(R¹)—COOH.

Examples of side chains of natural alph α amino acids include those of alanine, arginine, asparagine, aspartic acid, cysteine, cystine, glutamic acid, histidine, 5-hydroxylysine, 4-hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine, a-aminoadipic acid, α-amino-n-butyric acid, 3,4-dihydroxyphenylalanine, homoserine, α-methylserine, ornithine, pipecolic acid, and thyroxine.

Natural alpha-amino acids which contain functional substituents, for example amino, carboxyl, hydroxy, mercapto, guanidyl, imidazolyl, or indolyl groups in their characteristic side chains include arginine, lysine, glutamic acid, aspartic acid, tryptophan, histidine, serine, threonine, tyrosine, and cysteine. When R₃ in the compounds of the invention is one of those side chains, the functional substituent may optionally be protected.

The term “protected” when used in relation to a functional substituent in a side chain of a natural alpha-amino acid means a derivative of such a substituent which is substantially non-functional. For example, carboxyl groups may be esterified (for example as a C₁-C₆ alkyl ester), amino groups may be converted to amides (for example as a NHCOC₁-C₆ alkyl amide) or carbamates (for example as an NHC(═O)OC₁-C₆ alkyl or NHC(═O)OCH₂Ph carbamate), hydroxyl groups may be converted to ethers (for example an OC₁-C₆ alkyl or a O(C₁-C₆ alkyl)phenyl ether) or esters (for example a OC(═O)C₁-C₆ alkyl ester) and thiol groups may be converted to thioethers (for example a tert-butyl or benzyl thioether) or thioesters (for example a SC(═O)C₁-C₆ alkyl thioester).

Examples of side chains of non-natural alph α amino acids include those referred to below in the discussion of suitable R₃ groups for use in compounds of the present invention.

Salts of the compounds of the invention include physiologically acceptable acid addition salts for example hydrochlorides, hydrobromides, sulphates, methane sulphonates, p-toluenesulphonates, phosphates, acetates, citrates, succinates, lactates, tartrates, fumarates and maleates. Salts may also be formed with bases, for example sodium, potassium, magnesium, and calcium salts.

There are several chiral centres in the compounds according to the invention because of the presence of asymmetric carbon atoms. The presence of several asymmetric carbon atoms gives rise to a number of diastereomers with R or S stereochemistry at each chiral centre. In the compounds of the invention, the C atom carrying the hydroxamic acid and R₁ groups is predominantly in the S configuration, the C atom carrying the R₂ group is predominantly in the R configuration, and the C atom carrying the R₃ and R₄ groups is in either the R or S configuration, with the predominantly S configuration presently preferred.

As previously stated, the compounds with which the present invention is concerned are principally distinguished from the compounds disclosed in the prior patent publications listed above by the ester or thioester group R₄. Accordingly the groups R, R₁, R₁, R₂, and R₃, may include those which have been disclosed in the corresponding positions of compounds disclosed in any of those prior art patent publications listed above. Without limiting the generality of the foregoing, examples of substituents R, R₁, R₁, R₂, and R₃ are given below:

The Group R₁

R₁ may be, for example,

hydrogen, methyl, ethyl, n-propyl, n-butyl, isobutyl, hydroxyl, methoxy, allyl, phenylpropyl, phenylprop-2-enyl, thienylsulphanylmethyl, thienylsulphinylmethyl, or thienylsulphonylmethyl; or

C₁-C₄ alkyl, eg methyl, ethyl n-propyl or n-butyl, substituted by a phthalimido, 1,2-dimethyl-3,5-dioxo-1,2,4-triazolidin-4-yl, 3-methyl-2,5-dioxo-1-imidazolidinyl, 3,4,4-trimethyl-2,5-dioxo-1-imidazolidinyl, 2-methyl-3,5-dioxo-1,2,4-oxadiazol-4-yl, 3-methyl-2,4,5-trioxo-1-imidazolidinyl, 2,5-dioxo-3-phenyl-1-imidazolidinyl, 2-oxo-1-pyrrolidinyl, 2,5-dioxo-1-pyrrolidinyl or 2,6-dioxopiperidinyl, 5,5-dimethyl-2,4-dioxo-3-oxazolidinyl, hexahydro-1,3-dioxopyrazolo[1,2,a][1,2,4]-triazol-2-yl, or a naphththalimido (ie 1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl), 1,3-dihydro-1-oxo-2H-benz[f]isoindol-2-yl, 1,3-dihydro-1,3-dioxo-2H-pyrrolo[3,4-b]quinolin-2-yl, or 2,3-dihydro-1,3-dioxo-1H-benz[d,e]isoquinolin-2-yl group; or

cyclohexyl, cyclooctyl, cycloheptyl, cyclopentyl, cyclobutyl, cyclopropyl, tetrahydropyranyl or morpholinyl.

Presently preferred R₁ groups include n-propyl, allyl, methoxy and thienylsulfanylmethyl.

The Group R₂

R₂ may for example be

C₁-C₁₂ alkyl, C₃-C₆ alkenyl or C₃-C₆ alkynyl;

phenyl(C₁-C₆ alkyl)-, phenyl(C₃-C₆ alkenyl)- or phenyl(C₃-C₆ alkynyl)- optionally substituted in the phenyl ring;

heteroaryl(C₁-C₆ alkyl)-, heteroaryl(C₃-C₆ alkenyl)- or heteroaryl(C₃-C₆ alkynyl)- optionally substituted in the heteroaryl ring;

4-phenylphenyl(C₁-C₆ alkyl)-, 4-phenylphenyl(C₃-C₆ alkenyl)-, 4-phenylphenyl(C₃-C₆ alkynyl)-, 4-heteroarylphenyl(C₁-C₆ alkyl)-, 4-heteroarylphenyl(C₃-C₆ alkenyl)-, 4-heteroarylphenyl (C₃-C₆ alkynyl)-, optionally substituted in the terminal phenyl or heteroaryl ring;

phenoxy(C₁-C₆ alkyl)- or heteroaryloxy(C₁-C₆ alkyl)-optionally substituted in the phenyl or heteroaryl ring;

Specific examples of such groups include methyl, ethyl, n- and iso-propyl, n-, iso- and tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-nonyl, n-decyl, prop-2-yn-1-yl, 3-phenylprop-2-yn-1-yl, 3-(2-chlorophenyl)prop-2-yn-1-yl, phenylpropyl, 4-chlorophenylpropyl, 4-methylphenylpropyl, 4-methoxyphenylpropyl, phenoxybutyl, 3-(4-pyridylphenyl)propyl-, 3-(4-(4-pyridyl)phenyl )prop-2-yn-1-yl, 3-(4-phenylphenyl)propyl-, 3-(4-phenyl)phenyl)prop-2-yn-1-yl and 3-[(4-chlorophenyl)phenyl]propyl-.

Presently preferred R₂ groups include isobutyl, n-hexyl, 3-(2-chlorophenyl)prop-2-yn-1-yl.

The Group R₃

R₃ may for example be C₁-C₆ alkyl, phenyl, 2-, 3-, or 4-hydroxyphenyl, 2-, 3-, or 4-methoxyphenyl, 2-, 3-, or 4-pyridylmethyl, benzyl, 2-, 3-, or 4-hydroxybenzyl, 2-, 3-, or 4-benzyloxybenzyl, 2-, 3-, or 4-C₁-C₆ alkoxybenzyl, or benzyloxy(C₁-C₆alkyl)- group; or

the characterising group of natural α amino acid, in which any functional group may be protected, any amino group may be acylated and any carboxyl group present may be amidated; or

a group-[Alk]_(n)R₆ where Alk is a (C₁-C₆)alkyl or (C₂-C₆)alkenyl group optionally interrupted by one or more —O—, or —S— atoms or —N(R₇)- groups [where R₇ is a hydrogen atom or a (C₁-C₆)alkyl group], n is 0 or 1, and R₆ is an optionally substituted cycloalkyl or cycloalkenyl group; or

a benzyl group substituted in the phenyl ring by a group of formula —OCH₂COR₈ where R₈ is hydroxyl, amino, (C₁-C₆)alkoxy, phenyl(C₁-C₆)alkoxy, (C₁-C₆)alkylamino, di((C₁-C₆)alkyl)amino, phenyl(C₁-C₆)alkylamino, the residue of an amino acid or acid halide, ester or amide derivative thereof, said residue being linked via an amide bond, said amino acid being selected from glycine, α or β alanine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, serine, threonine, cysteine, methionine, asparagine, glutamine, lysine, histidine, arginine, glutamic acid, and aspartic acid; or

a heterocyclic(C₁-C₆)alkyl group, either being unsubstituted or mono- or di-substituted in the heterocyclic ring with halo, nitro, carboxy, (C₁-C₆)alkoxy, cyano, (C₁-C₆)alkanoyl, trifluoromethyl (C₁-C₆)alkyl, hydroxy, formyl, amino, (C₁-C₆)alkylamino, di-(C₁-C₆)alkylamino, mercapto, (C₁-C₆)alkylthio, hydroxy(C₁-C₆)alkyl, mercapto(C₁-C₆)alkyl or (C₁-C₆)alkylphenylmethyl; or

a group —CR_(a)R_(b)R_(c) in which:

each of R_(a), R_(b) and R_(c) is independently hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, (C₃-C₈)cycloalkyl; or

R_(c) is hydrogen and R_(a) and R_(b) are independently phenyl or heteroaryl such as pyridyl; or

R_(c) is hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or (C₃-C₈)cycloalkyl, and R_(a) and R_(b) together with the carbon atom to which they are attached form a 3 to 8 membered cycloalkyl or a 5- to 6-membered heterocyclic ring; or

R_(a), R_(b) and R_(c) together with the carbon atom to which they are attached form a tricyclic ring (for example adamantyl); or

R_(a) and R_(b) are each independently (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or a group as defined for R_(c) below other than hydrogen, or R_(a) and R_(b) together with the carbon atom to which they are attached form a cycloalkyl or heterocyclic ring, and R_(c) is hydrogen, —OH, —SH, halogen, —CN, —CO₂H, (C₁-C₄)perfluoroalkyl, —CH₂OH, —CO₂(C₁-C₆)alkyl, —O(C₁-C₆)alkyl, —O(C₂-C₆)alkenyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —S(C₂-C₆)alkenyl, —SO(C₂-C₆)alkenyl, —SO₂(C₂-C₆)alkenyl or a group —Q—W wherein Q represents a bond or —O—, —S—, —SO— or —SO₂— and W represents a phenyl, phenylalkyl, (C₃-C₈)cycloalkyl, (C₃-C₈)cycloalkylalkyl, (C₄-C₈)cycloalkenyl, (C₄-C₈)cycloalkenylalkyl, heteroaryl or heteroarylalkyl group, which group W may optionally be substituted by one or more substituents independently selected from, hydroxyl, halogen, —CN, —CO₂H, —CO₂(C₁-C₆)alkyl, —CONH₂, —CONH(C₁-C₆)alkyl, —CONH(C₁-C₆alkyl)₂, —CHO, —CH₂OH, (C₁-C₄)perfluoroalkyl, —O(C₁-C₆)alkyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —NO₂, —NH₂, —NH(C₁-C₆)alkyl, —N((C₁-C₆)alkyl)₂, —NHCO(C₁-C₆)alkyl, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, (C₃-C₈)cycloalkyl, (C₄-C₈)cycloalkenyl, phenyl or benzyl.

Examples of particular R₃ groups include benzyl, phenyl, cyclohexylmethyl, pyridin-3-ylmethyl, tert-butoxymethyl, iso-butyl, sec-butyl, tert-butyl, 1-benzylthio-1-methylethyl, 1-methylthio-1-methylethyl, and 1-mercapto-1-methylethyl.

Presently preferred R₃ groups include phenyl, benzyl, tert-butoxymethyl and iso-butyl.

The Group R₄

Examples of particular ester and thioester groups R₄ groups include those of formula —(C═O)OR₉, —(C═O)SR₉, —(C═S)SR₉, and —(C═S)OR₉ wherein R₉ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl, cycloalkyl, cycloalkyl(C₁-C₆)alkyl-, phenyl, heterocyclyl, phenyl(C₁-C₆)alkyl-, heterocyclyl(C₁-C₆)alkyl-, (C₁-C₆)alkoxy(C₁-C₆)alkyl-, (C₁-C₆)alkoxy(C₁-C₆)alkoxy(C₁-C₆)alkyl-, any of which may be substituted on a ring or non-ring carbon atom or on a ring heteroatom, if present. Examples of such R₉ groups include methyl, ethyl, n-and iso-propyl, n-, sec- and tert-butyl, 1-ethyl-prop-1-yl, 1-methyl-prop-1-yl, 1-methyl-but-1-yl, cyclopentyl, cyclohexyl, allyl, phenyl, benzyl, 2-, 3- and 4-pyridylmethyl, N-methylpiperidin-4-yl, 1-methylcyclopent-1yl, adamantyl, tetrahydrofuran-3-yl and methoxyethyl.

Presently preferred are compounds of formula (IB) wherein R₄ is a carboxylate ester of formula —(C═O)OR₉, wherein R₉ is benzyl, cyclopentyl, isopropyl or tert-butyl.

The Group R

Presently preferred R groups are hydrogen and methyl.

Specific examples of compounds of the invention include those prepared according to Examples 1-3 and 5-43 below, and salts, hydrates and solvates thereof. Compounds presently preferred for their potencies as inhibitors of proliferation of various rapidly dividing tumour cells are:

2S -(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid cyclopentyl ester,

2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid benzyl ester,

2S-{2R-[1S-Hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3-phenyl-propionic acid isopropyl ester,

2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-4-methyl-pentanoic acid cyclopentyl ester, and

pharmaceutically acceptable salts, hydrates and esters thereof.

Compounds according to the present invention wherein R₄ is a carboxylate ester group may be prepared by a process comprising causing an acid of general formula (II)

or an activated derivative thereof to react with hydroxylamine, O-protected hydroxylamine, or an N,O-diprotected hydroxylamine, or a salt thereof, R, R₁, R₂, R₃, and R₄ being as defined in general formula (I) except that any substituents in R₁, R₂, R₃, and R₄ which are potentially reactive with hydroxylamine, O-protected hydroxylamine, the N,O-diprotected hydroxylamine or their salts may themselves be protected from such reaction, then removing any protecting groups from the resultant hydroxamic acid moiety and from any protected substituents in R₁, R₂, R₃, and R₄.

Conversion of (II) to an activated derivative such as the pentafluorophenyl, hydroxysuccinyl, or hydroxybenzotriazolyl ester may be effected by reaction with the appropriate alcohol in the presence of a dehydrating agent such as dicyclohexyl dicarbodiimide (DCC), N,N-dimethylaminopropyl-N′-ethyl carbodiimide (EDO), or 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ).

Protecting groups as referred to above are well known per se, for example from the techniques of peptide chemistry. Amino groups are often protectable by benzyloxycarbonyl, t-butoxycarbonyl or acetyl groups, or in the form of a phthalimido group. Hydroxy groups are often protectable as readily cleavable ethers such as the t-butyl or benzyl ether, or as readily cleavable esters such as the acetate. Carboxy groups are often protectable as readily cleavable esters, such as the t-butyl or benzyl ester.

Examples of O-protected hydroxylamines for use in method (a) above include O-benzylhydroxylamine, O-4-methoxybenzylhydroxylamine, O-trimethylsilylhydroxylamine, and O-tert-butoxycarbonylhydroxylamine.

Examples of O,N-diprotected hydroxylamines for use in method (a) above include N,O-bis(benzyl)hydroxylamine, N,O-bis(4-methoxybenzyl)hydroxylamine, N-tert-butoxycarbonyl-O-tert-butyldimethylsilylhydroxylamine, N-tert-butoxycarbonyl-O-tetrahydropyranylhydroxylamine, and N,O-bis(tert-butoxycarbonyl)hydroxylamine.

Compounds of formula (II) may be prepared by a process comprising: coupling an acid of formula (III) or an activated derivative thereof with an amine of formula (IV)

wherein R, R₁, R₂, R₃, and R₄ are as defined in general formula (I) except that any substituents in R₁, R₂, R₃, and R₄ which are potentially reactive in the coupling reaction may themselves be protected from such reaction, and R₁₁ represents a hydroxy protecting group, and subsequently removing the protecting group R₁₁ and any protecting groups from R₁, R₂, R₃, and R₄.

Compounds of the invention wherein R₄ is a thioester may be prepared by coupling a compound of formula (IIIA) or an activated derivative thereof

wherein R₁ and R₂ are are as defined in general formula (I) and R₁₂ and R₁₃ are respectively N- and O-protecting groups, with a compound of formula (IV) above wherein R₄ is a thioester group, and selectively removing the O- and N-protecting groups from the hydroxamic acid group.

Active derivatives of acids (III) and (IIIA) include activated esters such as the pentafluorophenyl ester, acid anhydrides and acid halides, eg chlorides. Suitable hydroxy protecting groups may be selected from those known in the art.

Amino acid esters and thioesters of formula (IV) are either known or are prepared by routine known synthetic methods.

As mentioned above, compounds of formula (I) above, and those of formula (I) excluded by the provisos in the definition of formula (I) above, are useful in human or veterinary medicine since they are active as inhibitors of the proliferation of cancer cells. The utility of the invention therefore lies in the treatment of cancers, such as those caused by over-proliferation of lymphoma, leukemia, myeloma, adenocarcinoma, carcinoma, mesothelioma, teratocarcinoma, choriocarcinoma, small cell carcinoma, large cell carcinoma, melanoma, retinoblastoma, fibrosarcoma, leiomyosarcoma, glioblastoma or endothelioma cells. It will be understood that different compounds (I) will have differing potencies as proliferation inhibitors depending on the the type of cancer being treated. The activity of any particular compound (I) in inhibiting proliferation of any particular cell type may be routinely determined by standard methods, for example analagous to those described in the Biological Example herein. From the fact that compounds (I) which are poorly active as inhibitors of MMPs are nonetheless active in inhibiting proliferation of cancer cells, it is inferred that their utility in treating cancers is different from or supplementary to the utility of effective MMP inhibitors in the treatment of cancers.

In a further aspect of the invention there is provided a pharmaceutical or veterinary composition comprising a compound of the invention as defined by reference to formula (IB) above, together with a pharmaceutically or veterinarily acceptable excipient or carrier. One or more compounds of the invention may be present in the composition together with one or more excipient or carrier.

The compounds with which the invention is concerned may be prepared for administration by any route consistent with their pharmacokinetic properties.

Orally administrable compositions may be in the form of tablets, capsules, powders, granules, lozenges, liquid or gel preparations, such as oral, topical, or sterile parenteral solutions or suspensions. Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrrolidone; fillers for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricant, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, glucose syrup, gelatin hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters such as glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents.

For topical application to the skin, the drug may be made up into a cream, lotion or ointment. Cream or ointment formulations which may be used for the drug are conventional formulations well known in the art, for example as described in standard textbooks of pharmaceutics such as the British Pharmacopoeia.

The active ingredient may also be administered parenterally in a sterile medium. Depending on the vehicle and concentration used, the drug can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as a local anaesthetic, preservative and buffering agents can be dissolved in the vehicle.

It will be understood that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination and the severity of the particular disease undergoing therapy.

The following examples 1-3 and 5-43 illustrate embodiments of the invention. Example 4 describes the preparation of a compound for comparison with those of the invention. The following abbreviations have been used in the examples

DCM—Dichloromethane

DMF—N,N-Dimethylformamide

NMM—N-Methylmorpholine

TFA—Trifluoroacetic acid

HOBT—1-Hydroxybenzotriazole

Column chromatography was performed with flash grade silica gel. ¹H-NMR and ¹³C-NMR were recorded on a Bruker AC 250E spectrometer at 250.1 and 62.9 MHz respectively. CDCl₃ methanol-d₄ and dimethysulphoxide-d₆ (DMSO-d₆) were used as solvents and internal reference and spectra are reported as δ ppm from TMS.

EXAMPLE 1 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Methyl Ester

(a) 2S-(3S-tert-Butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Methyl Ester

A solution of L-phenylalanine methyl ester hydrochloride (3.9 g, 17.9 mmol) and NMM (2.0 mL, 17.9 mmol) in DMF (15 mL) was cooled in an ice-water bath and treated with 3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoic acid pentafluorophenyl ester (6.5 g, 14.9 mmol, WO 94/21625). The reaction was allowed to warm to room temperature and stirred overnight. The reaction mixture was concentrated under reduced pressure and the residue taken up in ethyl acetate and washed with 1M hydrochloric acid, 1M sodium carbonate and brine. The solution was dried over sodium sulphate, filtered and concentrated under reduced pressure to provide 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid methyl ester as a yellow solid (4.0 g, 52%). ¹H-NMR; δ (CDCl₃), 7.28-7.07 (5H, m), 6.58 (1H, d), 5.75-4.94 (1H, m), 5.07-4.75 (3H, m), 3.53 (3H, s), 3.13 (1H, dd), 2.97 (1H, dd), 2.45-2.22 (3H, m), 1.96-1.01 (2H, m), 1.38 (9H, s), 0.98-0.72 (2H, m) and 0.78-0.72 (6H, m).

(b) 2S-(3S-Hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Methyl Ester.

A solution of 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid methyl ester (4.0 g, 9.3 mmol) in a mixture of TFA and DCM (1:1, 10 mL) was allowed to stand at 5° C. overnight. The reaction mixture was concentrated under reduced pressure. Crystallisation of the product from ethyl acetate/hexane gave 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid methyl ester as a white solid (2.02 g, 58%). ¹H-NMR; δ (CDCl₃), 7.28-7.08 (5H, m), 5.57-5.42 (1H, m), 4.85-4.74 (3H, m), 3.68 (3H, s), 3.25 (1H, dd), 2.88 (1H, dd), 2.55 (2.42 (1H, m), 2.38-2.24 (1H, m), 1.90-1.75 (1H, m), 1.62-1.40 (3H, m), 1.08-0.92 (1H, m), 0.88 (3H, d) and 0.79 (3H, d).

(c) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Methyl Ester.

A solution of 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid methyl ester (2.02 g, 5.38 mmol) in DMF (15 mL) was cooled in an ice-water bath. N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (1.24 g, 5.38 mmol) and HOBT (873 mg, 6.46 mmol) were added with stirring. The reaction was allowed to warm to room temperature and after 2 hours a solution of hydroxylamine hydrochloride (561 mg, 8.07 mmol) and NMM (0.9 mL, 8.07 mmol) in DMF (5 mL) added. After stirring overnight the reaction mixture was concentrated under reduced pressure. The residue was treated with a 2:1 mixture of ether/water to precipitate a white solid. The product was recrystallised from methanol to yield 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid methyl ester as a white solid (309 mg, 15%). ¹H-NMR; δ (methanol-d₄), 8.67 (1H, d, J=7.7 Hz), 7.23-7.14 (5H, m), 5.45-5.32 (1H, m), 4.85-4.74 (3H, m), 3.68 (3H, s), 3.24-3.09 (1H, m), 2.91-2.66 (1H, m), 2.47-2.39 (1H, m), 2.01-1.76 (2H, m), 1.49-1.36 (3H, m), 1.09-0.95 (1H, m), 0.85 (3H, d, J=6.4 Hz) and 0.80 (3H, d, J=6.4 Hz); ¹³C-NMR; δ (methanol-d₄), 176.5, 173.3, 172.4, 138.4, 136.1, 130.2, 129.5, 128.0, 117.3, 65.3, 55.1, 55.0, 52.7, 41.6, 38.1, 35.7, 26.7, 24.6 and 21.6.

EXAMPLE 2 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Ethyl Ester

(a) 2S-(3S-tert-Butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Ethyl Ester.

A solution of L-phenylalanine ethyl ester (4.3 g, 22.0 mmol) in DMF (20 mL) was cooled in an ice-water bath and treated with 3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoic acid pentafluorophenyl ester (10.7 g, 24.0 mmol). The reaction was stirred at 35° C. overnight. The reaction mixture was concentrated under reduced pressure and the residue taken up in ethyl acetate and washed with 1M hydrochloric acid, 1M sodium carbonate and brine. The solution was dried over sodium sulphate, filtered and concentrated under reduced pressure to provide 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid ethyl ester as a yellow solid (13.7 g, used directly in (b)). ¹H-NMR; δ (CDCl₃), 7.35-7.12 (5H, m), 6.25 (1H, d), 5.84-5.50 (1H, m), 5.18-5.02 (1H, m), 4.99-4.89 (2H, m), 4.15-4.08 (2H, m), 3.20 (1H, dd), 3.06 (1H, dd), 2.52-2.32 (1H, m), 1.95-1.82 (2H, m), 1.72-1.55 (2H, m), 1.42 (9H, s), 1.28-1.21 (3H, m), 0.98-0.93 (2H, m) and 0.88-0.80 (6H, m).

(b) 2S-(3S-Hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Ethyl Ester

A solution of 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid ethyl ester (13.7 g, 31.0 mmol) in a mixture of TFA and DCM (1:1, 10 mL) was allowed to stand at room temperature overnight. The reaction mixture was concentrated under reduced pressure. Crystallisation of the product from ethyl acetate/hexane gave 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid ethyl ester as a white solid (1.5 g, 12%). ¹H-NMR; δ (CDCl₃), 7.35-7.28 (3H, m), 7.18-7.10 (2H, m), 6.22 (1H, d), 5.77-5.60 (1H, m), 5.08-4.99 (3H, m), 4.22 (2H, q), 3.24 (1H, dd), 3.07 (1H, dd), 2.61-2.52 (1H, m), 2.45-2.28 (2H, m), 2.08-1.94 (1H, m), 1.75-1.64 (1H, m), 1.60-1.45 (1H, m), 1.28 (3H, t), 1.21-1.09 (1H, m) and 0.86 (6H, d).

(c) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Ethyl Ester.

A solution of 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid ethyl ester (2.2 g, 5.38 mmol) in DMF (20 mL) was cooled in an ice-water bath. N-(3-dimethylamino propyl)-N′-ethylcarbodiimide hydrochloride (1.3 g, 6.78 mmol) and HOBT (916 mg, 6.78 mmol) were added with stirring. The reaction was allowed to warm to room temperature and after 2 hours a solution of hydroxylamine hydrochloride (589 mg, 8.48 mmol) and NMM (0.9 mL, 8.48 mmol) in DMF (10 mL) added. After stirring overnight the reaction mixture was concentrated under reduced pressure. The residue was treated with a 2:1 mixture of ether/water to precipitate a white solid which was collected by filtration and washed with hot ethyl acetate. Drying under vacuum provided 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid ethyl ester as a white solid (1.8 g, 79%). ¹H-NMR; δ (methanol-d₄), 8.65 (1H, d, J=8.4 Hz), 7.81-7.09 (5H, m), 5.45-5.32 (1H, m), 4.89-4.71 (3H, m), 4.13 (2H, q, J=7.1 Hz), 3.23-3.06 (2H, m), 2.48-2.38 (1H, m), 2.02-1.75 (3H, m), 1.51-1.30 (2H, m), 1.21 (3H, t, J=7.1 Hz), 1.01-0.90 (1H, m), 0.86 (3H, d, J=6.4 Hz) and 0.79 (3H, d, J=6.4 Hz); ¹³C-NMR; δ (methanol-d₄), 176.5, 172.9, 172.4, 138.4, 136.1, 130.3, 129.5, 128.0, 117.3, 65.1, 62.4, 56.5, 55.2, 55.1, 54.6, 43.4, 41.6, 38.2, 37.3, 35.7, 27.0, 26.6, 24.6, 21.7, 15.7 and 14.5.

EXAMPLE 3 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Isopropyl Ester

(a) 2S-(3S-tert-Butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Isopropyl Ester.

A solution of L-phenylalanine isopropyl ester (3.9 g, 18.8 mmol) in DMF (15 mL) was cooled in an ice-water bath and treated with 3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoic acid pentafluorophenyl ester (9.03 g, 20.7 mmol). The reaction was allowed to warm to room temperature and stirred overnight. The reaction mixture was concentrated under reduced pressure. The residue was taken up in ethyl acetate and washed with 1M hydrochloric acid, 1M sodium carbonate and brine. The solution was dried over sodium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography using a gradient elution of 100% DCM to 10% methanol/DCM. Product containing fractions were combined and solvent removed to yield 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid isopropyl ester as a yellow solid (3.5 g, 41%). ¹H-NMR; δ (CDCl₃), 7.44-7.15 (5H, m), 6.46 (1H, d), 5.72-5.48 (1H, m), 5.15-4.88 (3H, m), 3.25 (1H, dd), 3.11 (1H, dd), 2.60-2.48 (2H, m), 2.00-1.78 (1H, m), 1.72-1.58 (1H, m), 1.45 (9H, s), 1.35-1.18 (9H, m), 0.98-0.91 (1H, m) and 0.88-0.80 (6H, m).

(b) 2S-(3S-Hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Isopropyl Ester

A solution of 2S-(3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid isopropyl ester (3.5 g, 7.6 mmol) in a mixture of TFA and DCM (1:1, 10 mL) was allowed to stand at 5° C. overnight. The reaction mixture was concentrated under reduced pressure. Addition of ether to the residue gave 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid isopropyl ester as a white solid (261 mg, 8%). ¹H-NMR; δ (CDCl₃), 7.38-7.25 (3H, m), 7.18-7.12 (2H, m), 6.49 (1H, d), 5.70-5.55 (1H, m), 5.13-4.89 (3H, m), 3.24 (1H, dd), 3.05 (1H, dd), 2.63-2.45 (2H, m), 2.28-2.15 (1H, m), 2.02-1.79 (1H, m), 1.70-1.61 (1H, m), 1.58-1.40 (1H, m), 1.32-1.18 (7H, m), 0.98-0.91 (1H, m), 0.85-0.82 (6H, m).

(c) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Isopropyl Ester.

A solution of 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid isopropyl ester (260 mg, 0.64 mmol) in DMF (10 mL) was cooled in an ice-water bath. N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (148 mg, 0.77 mmol) and HOBT (104 mg, 0.77 mmol) were added with stirring. The reaction was allowed to warm to room temperature and after 2 hours a solution of hydroxylamine hydrochloride (67 mg, 0.96 mmol) and NMM (0.1 mL, 0.96 mmol) in DMF (5 mL) added. After stirring overnight the reaction mixture was concentrated under reduced pressure and t he product was purified by chromatography on acid-washed silica using 5-10% methanol in DCM. Recrystallisation from from ethyl acetate/hexane provided 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid isopropyl ester as a white solid (12 mg 4%). ¹H-NMR; δ (methanol-d₄), 8.64 (1H, d, J=8.2 Hz), 7.23-7.11 (5H, m), 5.41-5.34 (1H, m), 5.02-4.92 (1H, m), 4.85-4.69 (2H, m), 3.23-3.16 (1H, m), 2.89-2.80 (1H, m), 2.46-2.39 (1H, m), 2.01-1.79 (2H, m), 1.50-1.42 (2H, m), 1.23-1.56 (7H, m), 0.99-0.95 (1H, m), 0.86 (3H, d, J=6.3 Hz), and 0.80 (3H, d, J=6.4 Hz); ¹³C-NMR; δ (methanol-d₄), 176.4, 176.3, 138.4, 136.1, 130.3, 129.5, 123.0, 117.3, 70.2, 55.4, 41.6, 38.3, 35.7, 26.6, 24.5, 22.0, 21.9 and 21.7.

EXAMPLE 4 (For comparison) 3S-(2-Phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R, 5-dimethylhexanohydroxamic Acid

(a) 3S-(2-Phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-benzyloxycarbonyl-5-methylhexanoic Acid Benzyl Ester

A solution of 3S-hydroxycarbonyl-2-benzyloxycarbonyl-5-methylhexanoic acid benzyl ester (10.0 g, 25 mmol, WO 90/05719) in DMF (100 mL) was treated with HOBT (5.1 g, 38 mmol), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (5.9 g, 30 mmol), D-phenylalanine methyl ester (5.2 g, 29 mmol) and NMM (4.1 mL, 38 mmol). The yellow reaction mixture was stirred at room temperature overnight and concentrated under reduced pressure. The residue was taken up in ethyl acetate and washed with 1M hydrochloric acid (×2), saturated sodium bicarbonate (×2) and brine. The solution was dried over magnesium sulphate, filtered and concentrated to provide 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-benzyloxycarbonyl-5-methylhexanoic acid benzyl ester as colourless oil (12.2 g, 87%). ¹NMR; δ (CDCl₃), 7.41-7.17 (15H, m), 6.25 (1H, d, J=7.9 Hz), 5.22-5.04 (4H, m), 4.90-4.83 (1H, m), 3.86 (1H, d, J=10.1 Hz), 3.67 (3H, s), 3.11 (1H, dd, J=13.8, 5.6 Hz), 3.02-2.91 (2H, m), 1.69-1.54 (1H, m), 1.53-1.46 (1H, m), 1.05-0.96 (1H, m), 0.79 (3H, d, J=6.5 Hz) and 0.78 (3H, d, J=6.4 Hz).

(b) 3S-(2-Phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-methylene-5-methylhexanoic Acid

A solution of 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-benzyloxycarbonyl-5-methylhexanoic acid benzyl ester (3.4 g, 6.1 mmol) in ethanol (30 mL), was treated under an inert atmosphere with palladium catalyst (100 mg, 10% on charcoal) and then stirred under an atmosphere of hydrogen gas for 1 hour. The catalyst was removed by filtration through a glass fibre pad. The filtrate was treated with piperidine (0.7 mL) and formaldehyde (3.2 mL of a 37% wt aqeous solution, 7.05 mmol) and allowed to stand at room temperature overnight. The reaction mixture was concentrated under reduced pressure and the residue partitioned between ethyl acetate and saturated sodium bicarbonate solution. The aqueous layer was separated, acidified with 1M hydrochloric acid to pH 1 and extracted with ethyl acetate. The organic extracts were dried over magnesium sulphate, filtered and concentrated under reduced pressure to yield 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-methylene-5-methylhexanoic acid as a white solid (1.05 g, 50%). ¹NMR; δ (CDCl₃), 7.26-7.14 (3H, m), 7.06-7.02 (2H, m), 6.57 (1H, d, J=8.0), 6.44 (1H, s), 5.88 (1H, s), 4.93-4.81 (1H, m), 3.72 (3H, s), 3.54-3.48 (1H, m), 3.13 (1H, dd, J=13.9, 5.7 Hz), 3.02 (1H, dd, J=13.8, 6.4 Hz), 1.85-1.76 (1H, m), 1.58-1.41 (2H, m) and 0.90-0.85 (6H, m).

(c) 3S-(2-Phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R,5-dimethylhexanoic Acid

A solution of 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2-methylene-5-methylhexanoic acid (960 mg, 2.77 mmol) in ethanol was treated under an inert atmosphere with palladium catalyst (50 mg, 10% on charcoal). The reaction mixture was stirred under an atmosphere of hydrogen gas for 90 minutes. The catalyst was removed by filtration through a glass fibre pad. The filtrate was concentrated under reduced pressure to yield 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R,5-dimethylhexanoic acid as a white solid (900 mg, 93%). ¹NMR; δ (CDCl₃), 7.33-7.20 (3H, m), 7.15-7.11 (2H, m), 6.25 (1H, d, J=8.1 Hz), 4.99-4.90 (1H, m), 3.75 (3H, s), 3.19 (1H, dd, J=13.9, 5.5 Hz), 3.05 (1H, dd, J=14.0, 7.3 Hz), 2.63-2.54 (1H, m), 2.47-2.41 (1H, m), 1.73-1.61 (1H, m), 1.60-1.44 (1H, m), 1.20-1.10 (1H, m), 1.03 (3H, d, J=7.1 Hz), 0.86 (3H, d, J=6.5 Hz) and 0.85 (3H, d, J=6.5 Hz).

(d) 3S-(2-Phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R,5-dimethylhexanohydroxamic Acid

A solution of 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R,5-dimethylhexanoic acid (850 mg, 2.44 mmol), HOBT (395 mg, 2.92 mmol), O-benzylhydroxylamine (360 mg, 2.92 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (560 mg, 2.92 mmol) was stirred at room temperature for 96 hours. The reaction mixture was concentrated under reduced pressure to a colourless oil. The residue was taken up in ethyl acetate and washed with 2M hydrochloric acid (×2), saturated sodium bicarbonate (×2) and brine. The solution was dried over magnesium sulphate, filtered and concentrated under reduced pressure to a white solid. The solid was taken up in a 10% mixture of cyclohexene and ethanol (40 mL), treated with palladium catalyst (50 mg, 10% on charcoal) and heated at 80° C. for 1 hour. The catalyst was removed by filtration and the filtrate concentrated under reduced pressure. The product was taken up in methanol and ether added to provide 3S-(2-phenyl-1R-methylcarboxy-ethylcarbamoyl)-2R, 5-dimethylhexanohydroxamic acid as a white solid (340 mg, 38%). ¹H-NMR; δ (methanol-d₄), 8.57 (1H, d, J=8.3 Hz), 7.23-7.04 (5H, m), 4.71-4.64 (1H, m), 3.60 (3H, s), 3.14 (1H, dd, J=14.0, 4.8 Hz), 2.81 (1H, dd, J=14.0, 10.7 Hz), 2.35 (1H, dt, J=10.9, 3.0 Hz), 2.01-1.91 (1H, m), 1.43-1.29 (2H, m), 0.92-0.82 (1H, m), 0.78 (3H, d, J=6.4 Hz), 0.72 (3H, d, J=6.5 Hz), and 0.49 (3H, d, J=6.8 Hz); ¹³C-NMR; δ (methanol-d₄), 178.0, 174.7, 161.0, 131.6, 129.1, 54.0, 50.0, 43.3, 43.0, 39.5, 26.1, 25.8, 23.0, 18.2 and 17.6.

EXAMPLE 5 3R-(2-Phenyl-1S-methylcarboxy-ethylcarbamoyl)-2S, 5-dimethylhexanohydroxamic Acid

Using procedures similar to those described for example 4 and starting with 3R-hydroxycarbonyl-2-benzyloxycarbonyl-5-methylhexanoic acid benzyl ester (WO 90/05719) and L-phenylalanine methyl ester 3R-(2-phenyl-1S-methylcarboxy-ethylcarbamoyl)-2S, 5-dimethylhexanohydroxamic acid was prepared as a white solid. ¹H-NMR and ¹³C-NMR spectral data were directly analogous to those described for the enantiomer, example 4.

EXAMPLE 6 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenyl-propionic Acid Tert-butyl Ester

(a) 2S-[1R-(1S-tert-Butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic Acid Allyl Ester

A solution of 2S-allyl-3R-isobutyl-succinic acid 1-allyl ester (830 mg, 3.3 mmol, WO97/18183), HOBt (504 mg, 3.7 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (714 mg, 3.7 mmol) in DMF (10 mL) was stirred for 10 minutes. A suspension of L-phenylalanine tert butyl ester hydrochloride (800 mg, 3.1 mmol) and NMM (376 μL, 3.4 mmol) in DMF (5 mL) was added dropwise to the reaction mixture. The reaction mixture was stirred for 18 hours at room temperature. The reaction mixture was concentrated under reduced pressure. The residue was taken up in ethyl acetate and washed with 1M hydrochloric acid, saturated sodium bicarbonate and brine. The organic solution was dried over magnesium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography on silica gel eluting with a gradient of 9:1 to 2:1 hexane/ethyl acetate. Product containing fractions were combined and solvent removed under reduced pressure to leave 2S-[1R-(1S-tert-butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic acid allyl ester as a white solid (1.29 g, 91%). ¹H-NMR; δ (CDCl₃), 7.32-7.16 (5H, m), 5.99 (1H, d, J=8.1 Hz), 5.89 (1H, ddt, J=17.2, 10.4, 5.8 Hz), 5.69-5.53 (1H, m), 5.32 (1H, dq, J=17.2, 1.5 Hz), 5.23 (1H, ddd, J=10.4, 1.3, 1.2 Hz), 4.96-4.77 (3H, m), 4.56 (2H, dd, J=5.8, 1.1 Hz), 3.15-2.96 (2H, m), 2.66 (1H, dt, J=9.7, 5.1 Hz), 2.38 (1H, dt, J=10.4, 3.3 Hz), 2.11-1.90 (2H, m), 1.71-1.59 (1H, m), 1.53-1.41 (1H, m), 1.40 (9H, s), 1.07-0.94 (1H, m), 0.85 (3H, d, J=6.5 Hz) and 0.83 (3H, d, J=6.5 Hz).

(b) 2S-[1R-(1S-tert-Butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic Acid

A solution 2S-[1R-(1S-tert-butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic acid allyl ester (1.29 g, 2.82 mmol) in THF (15 mL) was treated with morpholine (300 μL) and tetrakis (triphenylphosphine) palladium (0) (40 mg) the reaction was allowed to stir at room temperature overnight. The reaction mixture was partitioned between ethyl acetate and 1M hydrochloric acid. The organic layer was dried over magnesium sulphate, filtered and concentrated under reduced pressure. The crude product was purified by column chromatography on silica gel eluting with 5% methanol in DCM. Product containing fractions were combined and solvent removed under reduced pressure to yield 2S-[1R-(1S-tert-butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic acid as a white solid (423 mg, 34%). ¹H-NMR; δ (CDCl₃), 7.34-7.20 (3H, m), 7.19-7.12 (2H, m), 6.20 (1H, d, J=7.9 Hz), 5.75-5.57 (1H, m), 4.79 (1H, dd, J=14.3, 6.5 Hz), 3.18 (1H, dd, J=14.0, 6.1 Hz), 3.03 (1H, dd, J=14.0, 6.8 Hz), 2.57-2.33 (3H, m), 2.08-1.94 (1H, m), 1.72-1.37 (2H, m), 1.44 (9H, s), 1.16 (1H, ddd, J=13.8, 9.8, 3.5 Hz) and 0.87-0.84 (6H, m).

(c) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenyl-propionic Acid Tert-butyl Ester

A solution of 2S-[1R-(1S-tert-butoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic acid (400 mg, 1.0 mmol), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (232 mg, 1.2 mmol) and HOBT (164 mg, 1.2 mmol) in DMF (10 mL) was stirred at 0° C. for 2 hours. Hydroxylamine hydrochloride (105 mg, 1.5 mmol) was taken up in DMF (2 mL) and NMM (166 μL, 1.5 mmol) added. After 10 minutes the hydroxylamine solution was added to the reaction mixture which was allowed to stir at room temperature for 18 hours. DMF was removed under reduced pressure and the residue partitioned between ethyl acetate and 1.0M hydrochloric acid. The organic layer was separated and washed with saturated sodium bicarbonate and brine before drying over magnesium sulphate. Filtration, evaporation and recrystallization from hot ethyl acetate yielded 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenyl-propionic acid tert-butyl ester as a white solid (248 mg, 64%). ¹H-NMR; δ (methanol-d₄), 8.52 (1H, d, J=8.4 Hz), 7.18-7.03 (5H, m), 5.34-5.28 (1H, m), 4.79-4.64 (2H, m), 4.62-4.55 (1H, m), 3.03 (1H, dd, J=13.9, 5.2 Hz), 2.77 (1H, dd, J=13.9, 10.5 Hz), 2.39-2.31 (1H, m), 1.96-1.85 (1H, m), 1.81-1.68 (1H, m), 1.44-1.22 (3H, m), 1.34 (9H, s), 0.94-0.89 (1H, m), 0.80 (3H, d, J=6.4 Hz) and 0.73 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.2, 172.4, 172.1, 138.4, 136.1, 130.3, 129.5, 127.9, 117.3, 82.8, 78.9, 55.8, 47.9, 41.6, 38.4, 35.7, 28.2, 26.6, 24.5 and 21.8.

EXAMPLE 7 2S-(2R-Hydroxycarbamoylmethyl-4-methyl-pentanoylamino)-3-phenyl-propionic Acid Isopropyl Ester

(a) 3R-(1S-sopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-hexanoic Acid Tert-butyl Ester

A solution of 3R-isobutyl-succinic acid 1-tert butyl ester (1.17 g, 5.1 mmol), L-phenylalanine isopropyl ester (1.17 g, 5.1 mmol), N-(3-dimethylaminopropyl)-N ′-ethylcarbodiimide hydrochloride (972 mg, 5.1 mmol), and HOBT (685 mg, 5.1 mmol) in ethyl acetate (30 mL) was heated under reflux for 18 hours. The reaction mixture was diluted with ethyl acetate and washed with 1M hydrochloric acid, saturated sodium bicarbonate and brine before drying over magnesium sulphate, filtration and concentration under reduced pressure to yield 3R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-hexanoic acid tert-butyl ester as a white solid (1.95 g, ˜100%). ¹H-NMR; δ (CDCl₃), 7.29-7.17 (5H, m), 6.23 (1H, d, J=7.8 Hz), 5.00-4.93 (1H, m), 4.80-4.78 (1H, m), 3.08-3.05 (2H, m), 2.60-2.49 (1H, m), 2.30-2.24 (1H, m),

A solution of 3R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-hexanoic acid tert-butyl ester (1.95 g, 4.9 mmol) in a 1:1 mixture of TFA:DCM (15 mL) was allowed to stand for 18 hours at room temperature. Solvent and excess TFA were removed under reduced pressure and the residue taken up in toluene and re-evaporated. 3R-(1S-Isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-hexanoic acid was produced as a colourless oil (1.9 g, contaminated with toluene). ¹H-NMR; δ (CDCl₃) 7.32-7.14 (5H, m), 6.61 (1H, bs), 5.07-4.96 (1H, m), 4.91-4.83 (1H, m), 3.10 (2H, d, J=6.1 Hz), 2.74-2.66 (1H, m), 2.55-2.42 (1H, m), 1.68-1.49 (3H, m), 1.24-1.18 (6H, m) and 0.88 (6H, 2xd).

(c) 2S-(2R-Hydroxycarbamoylmethyl-4-methyl-pentanoylamino)-3-phenyl-propionic Acid Isopropyl Ester.

A solution of 3R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-hexanoic acid (1.9 g, 5.23 mmol) was dissolved in DMF (15 mL), cooled in an ice-water bath and treated with HOBT (848 mg, 6.3 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (1.2 g, 6.3 mmol). After 1 hour a mixture of hydroxylamine hydrochloride (546 mg, 7.9 mmol) and NMM (794 mg, 7.9 mmol) in DMF (10 mL) was added. The reaction was stirred at room temperature for 96 hours. DMF was removed under reduced pressure and the residue partitioned between ethyl acetate and 2M hydrochloric acid. The organic layer was washed with distilled water, 5% aqueous sodium carbonate and water before drying over magnesium sulphate. The solution was filtered and concentrated under reduced pressure. Recrystallization from diethylether/hexane provided 2S-(2R-hydroxycarbamoylmethyl-4-methyl-pentanoylamino)-3-phenyl-propionic acid isopropyl ester as a white crystalline solid (270 mg, 14%). ¹H-NMR; δ (methanol-d₄), 7.17-7.10 (5H, m), 4.90-4.79 (1H, m), 4.55-4.49 (1H, m), 3.18-2.97 (1H, dd), 2.92-2.85 (1H, dd), 2.78-2.62 (1H, m), 2.02-1.93 (2H, m), 1.48-1.36 (2H, m), 1.11 (3H, d, J=6.3 Hz), 1.02 (3H, d, J=6.3 Hz), 1.00 (1H, m), 0.80 (3H, d, J=6.4 Hz) and 0.76 (3H, d, J=6.4 Hz). ¹³C-NMR; δ (methanol-d₄) 178.4, 173.8, 171.0, 139.6, 131.7, 130.8, 129.1, 71.4, 56.6, 43.3, 43.2, 41.2, 39.6, 38.3, 33.5, 28.2, 25.1, 23.6, 23.3 and 23.2.

EXAMPLE 8 2S-[2R-(S-Hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamine]-3-phenyl-propionic Acid Isopropyl Ester.

(a) 2S-[2R-(2,2-Dimethyl-5-oxo-[1,3]-dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic Acid Isopropyl Ester.

A solution of 2R-(2,2-dimethyl-5-oxo-[1,3-dioxolan-4S-yl)-4-methyl-pentanoic acid pentafluorophenyl ester (WO 95/19956) (2.87 g, 7.3 mmol) and L-phenylalanine isopropyl ester (1.5 g, 7.3 mmol) in DCM was allowed to stand at room temperature for 96 hours. The reaction mixture was diluted with DCM and washed with 1M aqueous sodium carbonate, 1M hydrochloric acid and brine before drying over magnesium sulphate, filtration and concentration under reduced pressure. The product was recrystallised from ethyl acetate/hexane to yield 2S-[2R-(2,2-dimethyl-5-oxo-[1,3]-dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic acid isopropyl ester as fine white needles (810 mg, 29%). ¹H-NMR; δ (CDCl₃), 7.35-7.17 (5H, m), 6.38 (1H, d, J=7.5 Hz), 5.06-4.99 (1H, m), 4.88-4.81 (1H, m), 4.50 (1H, d, J=5.9 Hz), 3.13-3.10 (2H, m), 2.73-2.65 (1H, m), 1.71-1.45 (3H, m), 1.57 (3H, s), 1.54 (3H, s), 1.22 (3H, d, J=6.2 Hz), 1.20 (3H, d, J=6.3 Hz), 0.90 (3H, d, J=6.1 Hz) and 0.88 (3H, d, J=6.2 Hz).

(b) 2S-[2R-(S-Hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamine]-3-phenyl-propionic Acid Isopropyl Ester.

A solution of sodium methoxide (325 mg, 6.1 mmol) and hydroxylamine hydrochloride (396 mg, 6.1 mmol) in methanol (15 mL) was stirred at room temperature for 2 hours. The solution was then filtered into a solution of 2S-[2R-(2,2-dimethyl-5-oxo-[1,3]-dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic acid isopropyl ester (800 mg, 2.1 mmol) in methanol (10 mL). The reaction was allowed to stand at room temperature for 18 hours. The reaction mixture was concentrated under reduced pressure and the residue partitioned between ethyl acetate and water. The organic layer was washed with water, dried over magnesium sulphate, filtered and concentrated under reduced pressure. Recrystallisation from ethyl acetate gave 2S-[2R-(S-hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamine]-3-phenyl-propionic acid isopropyl ester as white crystalline material which was dried under vacuum (465 mg, 58%). ¹H-NMR; δ (methanol-d₄), 7.17-7.12 (5H, m), 4.83-4.76 (1H, m), 4.53 (1H, t, J=7.2 Hz), 3.88 (1H, d, J=7.1 Hz), 2.95 (2H, d, J=7.1 Hz), 2.78-2.64 (1H, m), 1.55-1.29 (2H, m), 1.09 (3H, d, J=6.3 Hz), 1.08 (1H, m), 0.94 (3H, d, J=6.2 Hz), 0.81 (3H, d, J=6.5 Hz) and 0.76 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 175.7, 172.5, 171.5, 156.8, 138.0, 130.4, 129.4, 127.8, 73.2, 70.2, 55.4, 49.3, 39.2, 38.6, 26.6, 23.9, 22.1, 21.9 and 21.6.

EXAMPLE 9 2S-[2R-(1S-Hydroxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Isopropyl Ester

The title compound was prepared using procedures analogous to those described for example 4, starting with 2-benzyloxycarbonyl-3R-isobutyl-succinic acid 1-benzyl ester and L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.18-7.05 (5H, m), 4.94-4.84 (1H, m), 4.65 (1H, dd, J=10.41, 5.0 Hz), 3.11 (1H, dd, J=14.0, 5.2 Hz), 2.79 (1H, dd, J=13.9, 10.5 Hz), 2.35 (1H, dt, J=11.0, 3.1 Hz), 1.98-1.91 (1H, m), 1.45-1.35 (2H, m), 1.14 (3H, d, J=6.3 Hz), 1.08 (3H, d, J=6.2 Hz), 0.92-0.81 (1H, m), 0.79 (3H, d, J=6.4 Hz), 0.72 (3H, d, J=6.5 Hz) and 0.47 (3H, d, J=6.8 Hz). ¹³C-NMR; δ (methanol-d₄), 176.5, 160.8, 159.2, 138.4, 130.3, 129.5, 127.8, 70.2, 55.3, 53.5, 49.3, 41.9, 41.7, 36.3, 26.7, 24.5, 22.0, 21.7, 21.7 and 16.5.

EXAMPLE 10 2S-(2R-Hydroxycarbamoylmethyl-octanoylamino)-3-phenyl-propionic Acid Isopropyl Ester

The title compound was prepared using procedures analogous to those described for example 7, starting with 2R-n-hexylsuccinic acid 4-tert-butyl ester and L-phenylalanine isopropyl ester hydrochloride. ¹H-NMR δ (methanol-d₄), 7.19-7.09 (5H, m), 4.85-4.75 (1H, m), 4.50 (1H, dd, J=8.2, 6.9 Hz), 2.99 (1H, dd, J=13.7 6.7 Hz), 2.86 (1H, dd, J=13.7, 8.3 Hz), 2.68-2.52 (1H, m), 2.03-1.92 (2H, m), 1.48-1.25 (1H, m), 1.16-1.11 (9H, m), 1.10 (3H, d, J=6.3 Hz), 1.01 (3H, d, J=6.3 Hz) and 0.78 (3H, t, J=6.2 Hz). ¹³C-NMR; δ (methanol-d₄), 177.1, 172.5, 170.4, 138.2, 130.4, 129.5, 127.8, 70.1, 55.4, 43.7, 38.5, 36.4, 33.1, 32.8, 30.4, 28.1, 23.6, 22.0, 21.9 and 14.4.

EXAMPLE 11 2S-[2R-(S-Hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Cyclopentyl Ester

(a) 2S-[2R-(2,2-Dimethyl-5-oxo-[1,3]dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic Acid Cyclopentyl Ester.

A solution of 2R-(2,2-dimethyl-5-oxo-[1,3-dioxolan-4S-yl)-4-methyl-pentanoic acid pentafluorophenyl ester (WO95/19956) (1.93 g, 4.9 mmol) and L-phenylalanine cyclopentyl ester (1.16 g, 5.0 mmol) in ethyl acetate (50 mL) was heated under reflux for 2 hours. The reaction mixture was diluted with ethyl acetate and washed with 1M aqueous sodium carbonate, 1M hydrochloric acid and brine before drying over magnesium sulphate, filtration and concentration under reduced pressure. The product was purified by column chromatography on silica gel eluting with 5% methanol/DCM. Product containing fractions were combined and concentrated under reduced pressure to leave 2S-[2R-(2,2-dimethyl-5-oxo-[1,3]-dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic acid cyclopentyl ester as a white solid (305 mg, 28%). ¹H-NMR; δ (CDCl₃), 7.32-7.15 (5H, m), 6.42 (1H, d, J=7.5 Hz), 5.21-5.15 (1H, m), 4.87-4.80 (1H, m), 4.50 (1H, d, J=5.9 Hz), 3.11-3.08 (2H, m), (1H, m), 1.83-1.55 (11H, m), 1.58 (3H, s), 1.53 (3H, s), 0.89 (3H, d, J=6.0 Hz) and 0.88 (3H, d, J=6.1 Hz).

(b) 2S-[2R-(S-Hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Cyclopentyl Ester.

A solution of sodium methoxide (100 mg, 1.9 mmol) in methanol (3 mL) was treated with hydroxylamine hydrochloride (122 mg, 1.9 mmol) and allowed to stir at room temperature for 2 hours. The solution of methanolic hydroxylamine was then filtered into a solution of 2S-[2R-(2,2-dimethyl-5-oxo-[1,3]-dioxolan-4S-yl)-4-methyl-pentanoylamino]-3-phenylpropionic acid cyclopentyl ester in methanol (10 mL). The reaction was allowed to stir at room temperature for 18 hours. The reaction mixture was concentrated under reduced pressure and the residue redissolved in ethyl acetate. The solution was washed with 1M hydrochloric acid and brine, dried over magnesium sulphate, filtered and concentrated under reduced pressure. Recrystallisation from ethyl acetate/hexane provided 2S-[2R-(S-hydroxy-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid cyclopentyl ester as a white solid (55 mg, 18%). ¹H-NMR; δ (methanol-d₄), 8.23 (1H, d, J=7.3 Hz), 7.20-7.09 (5H, m), 5.99-5.95 (1H, m), 4.53 (1H, dd, J=14.6, 7.3 Hz), 3.88 (1H, d, J=7.0 Hz), 2.94 (2H, d, J=7.4 Hz), 2.73-2.64 (1H, m), 1.80-1.30 (10H, m), 1.09-1.01 (1H, m), 0.81 (3H, d, J=6.5 Hz) and 0.76 (3H, d, J=6.4 Hz). ¹³C-NMR; δ (methanol-d₄), 175.8, 172.8, 171.6, 138.0, 130.4, 129.5, 127.9, 79.6, 73.2, 55.4, 49.2, 39.1, 38.7, 33.5, 26.7, 24.6, 24.0 and 22.1.

EXAMPLE 12 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex--5-enoylamion)-3S-methyl-pentanoic Acid Cyclopentyl Ester

(a) N-Benzyloxycarbonyl-L-isoleucine Cyclopentyl Ester.

A solution of N-benzyloxycarbonyl-L-isoleucine (10.0 g, 37.7 mmol) in DCM 150 mL) was treated with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (7.94 g, 41.5 mmol), cyclopentanol (3.90 g, 45.2 mmol) and N,N-dimethylaminopyridine reaction mixture was washed with 1M hydrochloric acid, saturated sodium bicarbonate, and brine before drying over magnesium sulphate, filtration and removal of solvent under reduced pressure to leave N-benzyloxycarbonyl-L-isoleucine cyclopentyl ester as a colourless oil (10.99 g, 87%). ¹H-NMR; δ (CDCl₃) 7.44-7.30 (5H, m), 5.37-5.34 (1H, m), 5.22-5.18 (1H, 5.11 (2H, s), 4.33-4.27 (1H, m), 1.90-1.55 (10H, m), 1.51-1.35 (1H, m), 1.28-1.20 (2H, m), 0.93 (3H, d, J 6.9 Hz) and 0.91 (3H, d, J=7.0 Hz).

(b) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3S-methyl-pentanoic Acid Cyclopentyl Ester.

N-Benzyloxycarbonyl-L-isoleucine cyclopentyl ester was converted to the title compound using chemistry analogous to that described for example 6. ¹H-NMR; δ (methanol-d₄), 8.40 (1H, d, J=7.9 Hz), 5.64-5.47 (1H, m), 5.09-5.04 (1H, m), 4.93-4.85 (2H, m), 4.25-4.19 (1H, m), 2.56-2.49 (1H, m), 2.24-2.04 (2H, m), 1.98-1.88 (1H, m), 1.79-1.18 (12H, m), 1.22-1.120 (1H, m), 1.00-0.96 (1H, m) and 0.95-0.73 (12H, m). ¹³C-NMR; δ (methanol-d₄), 176.6, 172.6, 172.4, 165.9, 142.3, 136.0, 117.5, 79.3, 58.5, 47.7, 41.7, 37.9, 33.5, 26.8, 26.5, 24.6, 24.5, 21.8, 16.0 and 11.4.

EXAMPLE 13 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 2-methoxy-ethyl Ester

(a) N-(Carbobenzyloxy)-L-phenylalanine 2-methoxy-ethyl Ester.

A solution of N-(carbobenzyloxy)-L-phenylalanine (10.0 g, 33.4 mmol) in DMF (75 mL) was treated with HOBT (6.8 g, 50.1 mmol), N-(3-dimethylaminopropyl)-N ′-ethylcarbodiimide hydrochloride (7.7 g, 40.1 mmol), 2-methoxyethanol (2.8 g, 36.8 mmol) and a catalytic amount of 4-N,N-dimethylaminopyridine. The reaction was stirred overnight at room temperature. The reaction mixture was concentrated under reduced pressure and the residue taken up in ethyl acetate and washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The solution was dried over sodium sulphate, filtered and concentrated under reduced pressure to provide N-(carbobenzyloxy)-L-phenylalanine 2-methoxy-ethyl ester as a yellow foam (8.8 g, 74%). ¹H-NMR; δ (CDCl₃), 7.44-7.12 (10H, m), 5.27 (1H, d), 5.11 (2H, s), 4.72 (1H, dd), 4.26 (2H, m), 3.57 (2H, t), 3.38 (3H, s) and 3.15 (2H, m).

(b) L-Phenylalanine 2-methoxy-ethyl Ester.

A solution of N-(carbobenzyloxy)-L-phenylalanine 2-methoxy-ethyl ester (4.4 g, 12.3 mmol) in ethanol (75 mL) was treated with palladium on charcoal catalyst (440 mg, 10% Pd on charcoal) as a slurry in ethyl acetate (10 mL). Hydrogen gas was passed through the suspension for 3 hours. The reaction mixture was filtered and concentrated under reduced pressure to provide L-phenylalanine 2-methoxy-ethyl ester as a colourless oil (2.5 g, 92%). ¹H-NMR; d (methanol-d₄), 7.35-7.20 (5H, m), 4.27 (2H, m), 3.79 (1H, m), 3.57 (2H, m), 3.38 (3H, s), 3.10 (1H, dd), 2.90 (1H, dd) and 1.64 (2H, s).

(c) 2S-{1R-[1S-(2-Methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-pent-4-enoic Acid Tert-butyl Ester.

A solution of L-phenylalanine 2-methoxy-ethyl ester (910 mg, 4.1 mmol) in DMF (15 mL) was treated with 3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoic acid (1.0 g, 3.7 mmol), HOBT (750 mg, 5.6 mmol), N-(3-dimethylaminopropyl)-N ′-ethylcarbodiimide hydrochloride (850 mg, 4.4 mmol) and NMM (560 mg, 5.6 mmol). The reaction was stirred overnight at room temperature. The reaction mixture was concentrated under reduced pressure and the residue taken up in ethyl acetate. The solution was washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The solution was dried over sodium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography, eluting with 1-2% methanol/DCM. Product-containing fractions were combined and concentrated under reduced pressure to provide 2S-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-pent-4-enoic acid tert-butyl ester as an off-white gum (1.0 g, 58%). ¹H-NMR; δ (CDCl₃), 7.32-7.17 (5H, m), 6.00 (1H, d), 5.65 (1H, m), 4.98 (3H, m), 4.28 (2H, m), 3.56 (2H, m), 3.38 (3H, s), 3.20 (1H, dd), 3.07 (1H, dd), 2.45 (1H, m), 2.35 (1H, m), 1.97 (1H, m), 1.65 (1H, m), 1.49 (1H, m), 1.42 (9H, s), 1.06 (1H, m) and 0.85 (6H, 2xd).

(d) 2S-(3S-Hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 2-methoxy-ethyl Ester.

A solution of 2S-{1R-[1S-(2-methoxy-ethoxycarbony)-2-phenyl-ethylcarbamoy]-3-methyl-butyl}-pent-4-enoic acid tert-butyl ester (1.0 g, 2.1 mmol) in a mixture of TFA and DCM (1:1, 6 mL) was allowed to stand at 5° C. overnight. The reaction mixture was concentrated under reduced pressure and azeotroped with toluene. Crystallisation of the product from ethyl acetate/hexane gave 2S-(3S-hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid 2-methoxy-ethyl ester as a white solid (387 mg, 44%). ¹H-NMR; δ (CDCl₃), 7.33-7.13 (5H, m), 6.22 (1H,d), 5.65 (1H, m), 5.08-4.94 (3H, m), 4.38-4.24 (2H, m), 3.61 (2H, m), 3.40 (3H, s), 3.26 (1H, dd), 3.09 (1H, dd), 2.55 (1H, m), 2.41 (2H, m), 2.03 (1H, m), 1.66 (1H, dt), 1.49 (1H, m), 1.16 (1H, m) and 0.86 (6H, 2xd).

(e) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 2-methoxy-ethyl Ester.

A solution of 2S-(3S -hydroxycarbonyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid 2-methoxy-ethyl ester (375 mg, 0.9 mmol) in DMF (5 mL) was cooled in an ice/water bath. N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (205 mg, 117 mmol) and HOBT (145 mg, 1.1 mmol) were added with stirring. After 2 hours at this temperature, a solution of hydroxylamine hydrochloride (93 mg, 1.3 mmol) and NMM (136 mg, 1.3 mmol) in DMF (5 mL) was added. The reaction was allowed to warm to room temperature and stirred overnight. The reaction mixture was concentrated under reduced pressure and the residue partitioned between ethyl acetate and water. The organic phase was washed with 5% aqueous sodium carbonate and water, dried over sodium sulphate, filtered and concentrated under reduced pressure. The product was recrystallised from ethyl acetate/hexane to yield 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic ester as a white solid (185 mg, 48%). ¹H-NMR; δ (methanol-d₄), 7.20-7.05 (5H, m), 5.33 (1H, m), 4.79-4.67 (4H, m), 4.15 (2H, m), 3.48 (2H, m), 3.25 (3H, s), 3.15 (1H, m), 2.80 (1H, dd, J=10.9, 13.9 Hz), 2.37 (1H, dt, J=11.1, 3.2 Hz), 1.90 (1H, dt, J=11.4,3.4 Hz), 1.77 (1H, m), 1.44-1.18(3H, bm), 0.91 (1H, m), 0.79 (3H, d, J=6.4 Hz) and 0.72 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄) 176.4, 172.8, 172.4, 138.3, 136.1, 130.3, 129.5, 128.0, 117.3, 71.3, 65.2, 59.1, 55.0, 47.9, 41.6, 38.2, 35.7, 26.6, 24.6 and 21.6.

EXAMPLE 14 2S-[2R-(1S-Hydroxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid 2-methoxy-ethyl Ester

(a) 2-{1R-[1S-(2-Methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-malonic Acid Dibenzyl Ester.

A solution of 2-benzyloxycarbonyl-3R-isobutyl succinic acid 1-benzyl ester (4.06 g, 10.2 mmol), L-phenylalanine 2-methoxy-ethyl ester (see Example 13, 2.50 g, 11.2 mmol), HOBT (2.06 g, 15.3 mmol), N-methyl morpholine (1.54 g, 15.3 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (2.34 g, 12.2 mmol) in DMF (25 mL) was stirred at room temperature for 18 hours. The reaction mixture was concentrated under reduced pressure, the residue taken up in ethyl acetate and washed with 1M citric acid, saturated sodium hydrogen carbonate and brine. The solution was dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography, eluting with 2-3% methanol/DCM. Product-containing fractions were combined and concentrated under reduced pressure to provide 2-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-malonic acid dibenzyl ester (4.89 g, 80%). ¹H NMR; δ (CDCl₃), 7.39-7.13 (15H, bm), 6.30 (1H, d), 5.13 (3H, m), 4.90 (1H, m), 4.23 (2H, m), 3.86 (1H, d), 3.48 (3H, m), 3.35 (3H, s), 3.14 (1H, dd), 2.96 (2H, m), 1.68-1.45 (2H, m), 1.00 (1H, m), 0.78 (3H, d) and 0.77 (3H, d).

(b) 2-{1R-[1S-(2-Methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-acrylic Acid.

A solution of 2-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-malonic acid dibenzyl ester (4.88 g, 8.1 mmol) in ethanol (25 mL) was treated with palladium catalyst (490 mg, 10%Pd/charcoal) as a slurry in ethyl acetate (5 mL). Hydrogen gas was passed through the suspension for 2 hours. The reaction mixture was filtered and treated with piperidine (830 mg, 9.7 mmol) and formaldehyde (as a 37 weight percent solution in water, 0.79 mL, 9.7 mmol). The solution was allowed to stand at room temperature for 18 hours. The reaction mixture was concentrated under reduced pressure and the residue resuspended in ethyl acetate. The solution was washed with saturated sodium hydrogen carbonate. The aqueous phase was acidified to pH 1 with 1M hydrochloric acid and extracted with ethyl acetate. The organic phase was dried over sodium sulphate, filtered and concentrated under reduced pressure to provide 2-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-acrylic acid as a waxy white solid (2.21 g, 70%). ¹H NMR; δ (CDCl₃), 7.27-7.06 (5H, bm), 6.50 (1H, d), 6.43 (1H, s), 5.85 (1H, s), 4.92 (1H, m), 4.29 (2H, m), 3.59 (2H, t), 3.48 (1H, m), 3.39 (3H, s), 3.12 (2H, m), 1.79 (1H, m), 1.51 (2H, m), 0.90 (3H, d) and 0.87 (3H, d).

(c) 3R-[1S-(2-Methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-2S,5-dimethyl-hexanoic Acid.

A solution of 2-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl]-3-methyl-butyl}-acrylic acid (2.21 g, 5.65 mmol) in ethanol (40 mL) was treated with palladium catalyst (220 mg, 10%Pd/charcoal) as a slurry in ethyl acetate (5 mL). Hydrogen gas was passed through the suspension for 4 hours. The reaction mixture was filtered and concentrated under reduced pressure to provide 3R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl-2S,5-dimethyl-hexanoic acid (1.96 g, 88%). ¹H NMR; δ (CDCl₃), 7.31-7.14 (5H, m), 6.49 (1H, d), 5.55 (1H, bs), 4.98 (1H, m), 4.27 (2H, m), 3.57 (2H, m), 3.37 (3H, s), 3.19 (1H, dd), 3.07 (1H, m), 2.57 (1H, t), 2.44 (1H, m), 1.71-1.42 (2H, m), 1.11 (1H, m), 1.00 (2H, d), 0.85 (3H, d) and 0.84 (3H, d).

(d) 2S-[2R-(1S-Benzyloxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid 2-methoxy-ethyl Ester.

A solution of 3R-[1S-(2-methoxy-ethoxycarbonyl)-2-phenyl-ethylcarbamoyl}-2S,5-dimethyl-hexanoic acid (1.96 g, 5.0 mmol) in DMF (30 mL) was treated with HOBT (810 mg, 6.0 mmol), O-benzylhydroxylamine (740 mg, 6.0 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (1.15 g, 6.0 mmol) and stirred at ambient temperature for 48 hours. The reaction mixture was concentrated under reduced pressure and the residue dissolved in ethyl acetate. The solution was washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The solution was dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was recrystallised from ethyl acetate/hexane to provide 2S-[2R-(1S-benzyloxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid 2-methoxy-ethyl ester as a white solid (1.63 g, 66%). ¹H NMR; δ (CDCl₃), 9.21 (1H, s), 7.41-7.14 (10H, m), 6.37 (1H, d), 4.91 (3H, s), 4.27 (2H, m), 3.56 (2H, t), 3.36 (3H, s), 3.18 (1H, dd), 3.05 (1H, dd), 2.44 (1H, m), 2.18 (1H, m), 1.78 (1H, s), 1.47 (2H, m), 1.04 (1H, m), 0.85 (3H, d and 0.81 (3H, d).

(e) 2S-[2R-(1S-Hydroxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid 2-methoxy-ethyl Ester.

A solution of 2S-[2R-(1S-benzyloxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid 2-methoxy-ethyl ester (1.62 g, 3.3 mmol) in ethanol (30 mL) was treated with palladium catalyst (160 mg, 10%Pd/charcoal) as a slurry in ethyl acetate (5 mL). Hydrogen gas was passed through the suspension for 2 hours. The reaction mixture was filtered and concentrated under reduced pressure. The product was to provide 2S-[2R-(S-hydroxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid 2-methoxy-ethyl ester as a white solid (942 mg, 71%). ¹H-NMR; δ (methanol-d₄), 7.16-7.06 (5H, m), 4.70 (1H, m), 4.14 (2H, t, J=4.7 Hz), 3.47 (2H, m), 3.25 (3H, s), 3.18 (1H, m), 2.82 (1H, dd, J=10.5, 13.9 Hz), 2.34 (1H, m), 1.94 (1H, m), 1.40 (2H, m), 0.89 (1H, m), 0.89 (1H, m), 0.78 (3H, d, J=6.4 Hz), 0.72 (3H, d, J=6.4 Hz) and 0.48 (3H, d, J=6.8 Hz). ¹³ C-NMR; δ (methanol-d₄), 176.6, 174.4, 172.8, 138.4, 130.3, 129.5, 127.8, 78.8, 71.3, 65.2, 59.1, 55.1, 48.6, 42.0, 41.7, 36.3, 26.8, 24.6, 21.7 and 16.5.

EXAMPLE 15 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hexanoylamino)-3,3-dimethyl-butyric Acid 2-methoxy-ethyl Ester

(a) 2S-{1R-[1S-(2-Methoxy-ethoxycarbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic Acid tert-butyl Ester.

L-tert-Leucine 2-methoxy-ethyl ester (840 mg, 4.4 mmol), which had been prepared in a similar way to L-phenylalanine 2-methoxy-ethyl ester (example 13) was dissolved in DMF (15 mL). This solution was treated with 3S-tert-butoxycarbonyl-2R-isobutyl-hex-5-enoic acid (1.09 g, 4.0 mmol), HOBT (820 mg, 6.1 mmol), NMM (610 mg, 6.1 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (930 mg, 4.9 mmol) and stirred at ambient temperature for 18 hours. The reaction mixture was concentrated under reduced pressure and the residue taken up in ethyl acetate. The solution was washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The organic phase was dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography, eluting with 1% methanol/DCM. Product-containing fractions were combined and concentrated under reduced pressure to provide 2S-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic acid tert-butyl ester as an off-white solid (1.02 g, 57%). ¹H NMR; δ CDCl₃), 6.14 (1H,d), 5.73 (1H, m), 5.04 (2H, m), 4.48 (1H,d), 4.28 (2H, m), 3.59 (2H, t), 3.36 (3H, s), 2.49 (3H,m), 2.26 (2H, m), 1.68 (1H, m), 1.47 (9H, m), 1.12 (2H, m), 1.09 (9H, s) 0.90 (3H, d) and 0.86 (3H, d).

(b) 2S-{1R-[1S-(2-Methoxy-ethoxycarbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic Acid.

A solution of 2S-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic acid tert-butyl ester (1.00 g, 2.3 mmol) in a mixture of TFA and DCM (1:1, 6 mL) was allowed to stand at 5° C. overnight. The reaction mixture was concentrated under reduced pressure and azeotroped with ethyl acetate and toluene to leave 2S-{1R-[1S-(2-methoxy-ethoxycarbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic acid as a yellow gum (870 mg, quantitative). ¹H-NMR; δ (methanol-d₄), 8.21 (1H, d), 5.64 (1H, m), 4.92 (3H, m), 4.26 (1H, d), 4.14 (2H, m), 3.49 (2H, m), 3.24 (3H, s), 2.67 (1H, m), 2.67 (1H, m), 2.44 (1H, m), 2.16 (3H, m), 1.60-1.32 (3H, m), 1.02 (1H, m), 0.91 (9H, m) and 0.77 (6H, m).

(c) 2S-(3S-Benzyloxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric Acid 2-methoxy-ethyl Ester.

A solution of 2S-{1R-[1S-(2-methoxy-ethoxy carbonyl)-2,2-dimethyl-propylcarbamoyl]-3-methyl-butyl}-pent-4-enoic acid (463 mg, 1.2 mmol) in DMF (5 mL) was treated with HOBT (195 mg, 1.4 mmol), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (276 mg, 1.4 mmol) and O-benzylhydroxylamine (177 mg, 1.4 mmol). The reaction was stirred at ambient temperature for 18 hours. The reaction mixture was concentrated under reduced pressure and taken up in ethyl acetate. The solution was washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The organic phase was dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was recrystallised from ethyl acetate/hexane to provide 2S-(3S-benzyloxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric acid 2-methoxy-ethyl ester as a white solid (106 mg, 18%). ¹H NMR; δ (CDCl₃), 9.03 (1H, s), 7.42-7.34 (5H, m), 6.26 (1H, d), 5.65 (1H, m), 4.97 (4H, m), 4.42 (1H, d), 4.28 (2H, m), 3.58 (2H, t), 3.35 (3H, s), 2.57-2.26 (4H, m), 1.47 (2H, m), 1.11 (1H, m), 1.00 (9H, m), 0.89 (3H, d) and 0.83 (3H, d).

(d) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hexanoylamino)-3,3-dimethyl-butyric Acid 2-methoxy-ethyl Ester.

A solution of 2S-(3S-benzyloxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric acid 2-methoxy-ethyl ester (95 mg, 0.2 mmol) in ethanol (20 mL) was treated with palladium catalyst (10 mg, 10%Pd/charcoal) as a slurry in ethyl acetate (3 mL). Hydrogen gas was passed through the suspension for 4 hours. The reaction mixture was filtered and concentrated under reduced pressure. The product was purified by preparative HPLC using a C₁₈ silica column, eluting with 70% methanol/30% water (containing 0.1% TFA). Product-containing fractions were combined and concentrated under reduced pressure. The product was dissolved in DCM and washed with saturated sodium hydrogen carbonate. The organic solution was dried with sodium sulphate, filtered and concentrated under reduced pressure to provide 2S-(3S-hydroxycarbamoyl-2R-isobutyl-hexanoylamino)-3,3-dimethyl-butyric acid 2-methoxy-ethyl ester as a white solid (40 mg, 52%). ¹H-NMR; δ (methanol-d₄), 8.28 (1H, d, J=8.7 Hz), 4.27 (1H, d, J=8.8 Hz), 4.14 (2H, m), 3.49 (2H, t, J=4.7 Hz), 3.24 (3H, s), 2.57 (1H, dt, J=10.9, 3.1 Hz), 2.07 (1H, m), 1.50-0.99 (7H, bm), 0.95 (9H, s) and 0.91-0.72 (9H, m). ¹³C-NMR; δ (methanol-d₄), 177.0, 173.2, 172.2, 71.4, 64.6, 62.6, 62.5, 58.9, 47.9, 47.8, 41.8, 34.9, 34.3, 27.3, 26.8, 24.5, 21.8, 21.5 and 14.3.

EXAMPLE 16 2S-[2R-(S-Hydroxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Isopropyl Ester

(a) 2R-(S-Benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoic Acid.

A solution of 3R-isobutyl-4S-methoxy-dihydrofuran-2,5-dione (WO 97/02239) (609 mg, 3.27 mmol), and O-benzylhydroxylamine (403 mg, 3.27 mmol) in ethyl acetate (5 mL) was stirred at room temperature for 1 hour. The reaction mixture was concentrated under reduced pressure to provide 2R-(S-benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoic acid as a white foam (1.01 g, 100%). ¹H NMR; δ (CDCl₃), 7.43-7.36 (5H, m), 5.00-4.89 (2H, m), 3.90 (1H, d, J=6.0 Hz), 3.34 (3H, s), 2.91-2.84 (1H, m), 1.74-1.65 (2H, m), 1.35-1.24 (1H, m), 0.94-0.89 (6H, 2xd).

(b) 2S-[2R-(S-Benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Isopropyl Ester.

A solution of 2R-(S-benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoic acid (1.01 g, 3.3 mmol) in tetrahydrofuran (15 mL) at 0° C. was treated with L-phenylalanine isopropyl ester (810 mg, 3.9 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (750 mg, 3.9 mmol). The reaction mixture was allowed to warm to ambient temperature and stirred for 18 hours. The solution was concentrated under reduced pressure and the residue taken up in DCM. This solution was washed with 1M hydrochloric acid, saturated sodium hydrogen carbonate and brine. The organic phase was dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was purified by column chromatography, eluting with 2% methanol/DCM. Product-containing fractions were combined and concentrated under reduced pressure to provide 2S-[2R-(S-benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid isopropyl ester as a white solid (1.39 g, 85%). ¹H NMR; δ (methanol-d₄), 7.35-7.08 (10H, m), 4.83 (1H, m), 4.79 (2H, s), 4.58 (1H, m), 3.32 (1H, d), 3.00 (1H, m), 2.94 (3H, s), 2.86 (1H, m), 2.59 (1H, m), 1.36 (2H, m), 1.14 (1H, m), 1.07 (6H, dd), 0.77 (3H, d) and 0.72 (3H, d).

(c) 2S-[2R-(S-Hydroxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Isopropyl Ester.

A solution of 2S-[2R-(S-benzyloxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid isopropyl ester (1.37 g, 2.8 mmol) in ethanol (30 mL) was treated with palladium catalyst (274 mg, 10%Pd/charcoal) as a slurry in ethyl acetate (5 mL). Hydrogen gas was passed through the suspension for 2 hours. The reaction mixture was filtered and concentrated under reduced pressure. The product was recrystallised from ethyl acetate/hexane to provide 2S-[2R-(S-hydroxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic acid isopropyl ester as a white solid (778 mg, 70%). ¹H-NMR; δ (methanol-d₄), 7.12 (5H, m), 4.85 (1H, m), 4.59 (1H, dd, J=8.2, 6.2 Hz), 3.39 (1H, d, J=9.7 Hz), 3.02 (3H, s), 2.92 (2H, m), 2.63 (1H, dt, J=11.1, 3.4 Hz), 1.44 (2H, m), 1.11(3H, d, J=6.2 Hz), 1.03 (3H, d, J=6.3 Hz), 0.87 (1H, m), 0.80 (3H, d, J=6.4 Hz) and 0.75 (3H, d, J=6.4 Hz), ¹³C-NMR; δ (methanol-d₄), 175.3, 172.4, 169.4, 138.2, 130.3, 129.4, 127.7, 82.8, 70.1, 58.0, 55.4, 48.7, 38.4, 26.5, 24.3, 22.0, 21.9 and 21.8.

EXAMPLE 17 2S-{2R-[1S-Hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3-phenyl-propionic Acid Isopropyl Ester

(a) 3R-(1S-Isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-2S-(thiophen-2-ylsulphanylmethyl)-hexanoic Acid.

A solution of 2-[1R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-acrylic acid (intermediate in example 5) (1.67 g, 4.5 mmol) in propan-2-ol (5 mL) was treated with 2-mercaptothiophene (1.03 g, 8.9 mmol). The reaction mixture was heated at 60° C. in the dark for 72 hours. The solution was concentrated under reduced pressure. The product was purified by column chromatography, eluting with 1% methanol/DCM. Product-containing fractions were combined and concentrated under reduced pressure to provide 3R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-2S-(thiophen-2-ylsulphanylmethyl)-hexanoic acid as an off-white foam (1.08 g, 49%). ¹H NMR; δ (CDCl₃), 7.36-7.27 (4H, m), 7.18 (2H, m), 7.05 (1H, m), 7.00 (1H, m), 6.35 (1H, d), 5.07 (1H, m), 4.85 (1H, m), 3.23 (2H, m), 3.08 (1H, dd), 2.79-2.59 (3H, m), 1.59 (2H, m), 1.25 (6H, t), 1.17 (1H, m) and 0.86 (6H, 2xd).

(b) 2S-{2R-[1S-Hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3-phenyl-propionic Acid Isopropyl Ester.

A solution of 3R-(1S-isopropoxycarbonyl-2-phenyl-ethylcarbamoyl)-5-methyl-2S-(thiophen-2-ylsulphanylmethyl)-hexanoic acid (1.06 g, 2.2 mmol) in DMF (6 mL) was treated with HOBT (350 mg, 2.6 mmol) and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (497 mg, 2.6 mmol). The solution was stirred in an ice/water bath for 2 hours and then treated with a pre-mixed solution of hydroxylamine hydrochloride (225 mg, 3.2 mmol) and NMM (328 mg, 3.2 mmol) in DMF (5 mL). The reaction mixture was stirred at ambient temperature for 96 hours. The solution was concentrated under reduced pressure and the residue taken up in ethyl acetate and partitioned with water. The organic phase was washed with 0.5M sodium carbonate and water, dried with sodium sulphate, filtered and concentrated under reduced pressure. The product was recrystallised from ethyl acetate/hexane to provide 2S-{2R-[1S-hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3-phenyl-propionic acid isopropyl ester as a white solid (707 mg, 65%). ¹H-NMR; δ (methanol-d₄), 7.29 (1H, dd, J=1.5, 5.0 Hz), 7.13 (5H, m), 6.89-6.83 (2H, m), 4.88 (1H, m), 4.61 (1H, dd, J=4.6, 11.0 Hz), 3.12 (1H, dd, J=4.6, 13.9 Hz), 2.74 (1H, dd, J=11.1, 13.9 Hz), 2.33 (2H, m), 2.13 (1H, m), 1.90 (1H, dd, J=3.3, 13.2 Hz), 1.42-1.33 (2H, m), 1.14 (3H, d, J=6.3 Hz), 1.10 (3H, d, J=6.2 Hz), 0.90 (1H, m), 0.78 (3H, d, J=6.4 Hz) and 0.72 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d4), 175.4, 172.3, 171.0, 138.2, 134.3, 130.1, 129.6, 128.5, 128.2, 70.3, 55.2, 47.9, 47.8, 41.6, 39.0, 38.2, 26.4, 24.4, 21.9 and 21.6.

EXAMPLE 18 2S-[2-R-(1S-Hydroxycarbamoyl-ethyl)-4-methyl-pentanoylamino]-3,3-dimethyl-butyric Acid 2-methoxy-ethyl Ester

The title compound was prepared using an analogous route to that described for example 14 replacing L-phenylalanine with L-tert-leucine. ¹H-NMR; δ (methanol-d₄), 4.26 (1H, s), 4.14 (2H, m), 3.50 (2H, m), 3.24 (3H, s), 2.60 (1H, dt, J=10.8, 3.2 Hz), 2.15 (1H, m), 1.49-1.19 (3H, m), 0.98 (3H, s), 0.95 (9H, s), 0.81 (3H, d, J=6.4 Hz) and 0.73 (3H, dd, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.9, 174.4, 172.2, 71.4, 64.6, 62.5, 58.9, 48.4, 42.1, 42.0, 34.8, 27.3, 26.9, 24.5, 21.8 and 17.0.

EXAMPLE 19 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric Acid 2-methoxy-ethyl Ester

The title compound was prepared using an analogous route to that described for example 13 replacing L-phenylalanine with L-tert-leucine. ¹H-NMR; δ (methanol-d₄), 8.28 (1H, d, J=8.6 Hz), 5.54 (1H, m), 4.88 (2H, m), 4.26 (1H, m), 4.14 (2H, m), 4.07 (2H, m), 3.24 (3H, s), 2.62 (1H, m), 2.17-1.95 (3H, bm), 1.44-1.18 (3H, bm), 1.00 (1H, m), 0.95 (9H, s), 0.81 (3H, d, J=6.4 Hz) and 0.73 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.8, 172.4, 172.1, 136.0, 117.5, 71.3, 64.6, 62.7, 62.6, 58.9, 48.3, 47.6, 41.8, 36.3, 35.1, 34.8, 30.7, 27.3, 26.8, 24.5 and 21.8.

EXAMPLE 20 2S-(3-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 replacing L-phenylalanine isopropylester with L-phenylalanine cyclopentylester. ¹H-NMR; δ (methanol-d₄), 7.18-7.02 (5H, m), 5.32 (1H, m), 5.06 (1H, m), 4.79-4.63 (3H, m), 3.10 (1H, dd, J=14.0, 5.1 Hz), 2.78 (1H, dd, J=13.9, 10.6 Hz), 2.36 (1H, dt, J=11.1, 3.0 Hz), 1.90 (1H, dt, J=11.6, 3.4 Hz), 1.80-1.16 (13H, bm), 0.89 (1H, m), 0.79 (3H, d, J=6.4 Hz) and 0.73 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.3, 172.7, 172.4, 138.3, 136.1, 130.2, 129.5, 128.0, 117.3, 79.6, 55.2, 47.9, 47.8, 41.6, 38.3, 35.7, 33.5, 26.6, 24.7, 24.5 and 21.7.

EXAMPLE 21 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hexanoylamino)-3-phenylpropionic Acid Isopropyl Ester

The title compound was prepared by an analogous route to that described for example 15. ¹H-NMR; δ (methanol-d₄), 7.18-7.06 (5H, m), 4.90 (1H, sept, J=6.3 Hz), 4.64 (1H, dd, J=4.8, 10.7 Hz), 3.10 (1H, dd, J=4.8, 14.0 Hz), 2.79 (1H, dd, J=10.6, 14.0 Hz), 2.35 (1H, dt, J=3.3, 11.2 Hz), 1.89 (1H, dt, J=3.3, 11.0 Hz), 1.39 (2H, m), 1.15 (3H, d, J=6.3 Hz), 1.09 (3H, d, J=6.3 Hz), 1.06-0.83 (4H, m), 0.80 (3H, d, J=6.5 Hz), 0.73 (3H, d, J=6.6 Hz), 0.58 (3H, t, J=7.2 Hz) and 0.50 (1H, m). ^(13 C-NMR; δ (methanol-d) ₄), 176.6, 173.2, 172.5, 138.5, 130.2, 129.5, 127.9, 70.2, 55.3, 48.1, 47.4, 41.7, 38.3, 33.2, 26.5, 24.6, 22.0, 21.9, 21.7, 21.2 and 14.0.

EXAMPLE 22 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric Acid Isopropyl Ester

The title compound was prepared using an analogous route to that described for example 3 replacing L-phenylalanine with L-tert-leucine. ¹H-NMR; δ (methanol-d₄), 5.56 (1H, m), 4.89 (3H, m), 4.20 (1H, m), 2.60 (1H, m), 2.21-1.93 (3H, bm), 1.50-1.24 (2H, m), 1.15 (6H, d, J=6.3 Hz), 1.00 (1H, m), 0.94 (9H, s), 0.82 (3H, d, J=6.5 Hz) and 0.73 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.7, 172.4, 171.7, 136.0, 117.5, 69.9, 62.7, 48.1, 47.6, 41.8, 36.3, 34.7, 27.3, 26.8, 24.5, 22.0 and 21.9.

EXAMPLE 23 2R-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Isopropyl Ester

The title compound was prepared using an analogous route to that described for example 3 replacing L-phenylalanine isopropylester with D-phenylalanine isopropylester. ¹H-NMR; δ (methanol-d₄), 7.11 (5H, m), 5.52 (1H, m), 4.89 (3H, m), 4.66 (1H, dd, J=11.0, 4.6 Hz), 3.15 (1H, dd, J=14.1, 4.6 Hz), 2.75 (1H, dd, J=14.1, 11.1 Hz), 2.34 (1H, m), 2.16 (2H, m), 2.08 (1H, m), 1.27 (1H, m), 1.15 (3H, d, J=14.0, 6.3 Hz), 1.10 (3H, d, J=6.3 Hz), 0.69 (2H, m) and 0.52 (6H, d, J=5.0 Hz). ¹³C-NMR; δ (methanol-d₄), 176.6, 172.5, 172.4, 138.4, 136.3, 130.1, 129.5, 127.8, 117.4, 70.3, 55.2, 48.4, 47.8, 41.0, 38.2, 36.1, 26.3, 24.4, 22.0 and 21.6.

EXAMPLE 24 2S-[2R-(S-Hydroxycarbamoyl-methoxy-methyl)-4-methyl-pentanoylamino]-3,3-dimethyl-butyric Acid Isopropyl Ester

The title compound was prepared using an analogous route to that described for example 16 replacing L-phenylalanine with L-tert-leucine. ¹H-NMR; δ (methanol-d₄), 4.92 (1H, m), 4.25 (1H, m), 3.42 (1H, d, J=9.8 Hz), 3.13 (3H, s), 2.77 (1H, m), 1.50-1.24 (2H, m), 1.15 (6H, d, J=6.3 Hz), 0.92 (9H, s), 0.87 (1H, m), 0.81 (3H, d, J=6.5 Hz) and 0.76 (3H, d, J=6.6 Hz). ¹³C-NMR; δ (methanol-d₄), 175.3, 171.7, 169.5, 82.9, 69.8, 62.3, 62.2, 58.0, 48.7, 38.3, 35.3, 27.1, 26.9, 24.2, 22.0 and 21.9.

EXAMPLE 25 2S-{(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoyl)-methyl-amino)-3-phenylpropionic Acid Isopropyl Ester

The title compound was prepared using an analogous route to that described for example 3 using N-methyl-L-phenylalanine isopropyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.18-7.00 (5H, m), 5.45 (1H, dd, J=11.8, 4.7 Hz), 5.34-5.17 (1H, m), 5.01-5.91(1H, m), 4.85-4.66 (2H, m), 3.30 (1H, dd, J=14.6, 4.6 Hz), 3.02-2.84 (4H, m+s), 1.96-1.86 (1H, m), 1.68-1.50 (1H, m), 1.49-1.34 (2H, m), 1.16 (3H, d, J=6.2 Hz), 1.15 (3H, d, J=6.3 Hz), 1.01-1.10 (2H, m), 0.76 (3H, d, J=6.4, 6.5 Hz), 0.74 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 177.6, 172.4, 171.2, 128.2, 136.1, 130.1, 129.5, 128.1, 117.4, 70.4, 60.0, 42.8, 42.3, 35.3, 34.8, 33.8, 26.4, 24.5, 22.5, 22.0.

EXAMPLE 26 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Benzyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine benzyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.39-7.19 (10H, m), 5.44 (1H, m), 5.20 (2H, s), 4.89 (3H, m), 3.28 (1H, m), 2.95 (1H, dd, J=13.8, 10.8 Hz), 2.48 (1H, m), 2.03 (1H, dt, J=11.3, 3.2 Hz), 1.88 (1H, m), 1.45 (3H, m) 0.98 (1H, m), 0.81 (3H, d, J=H=6.4 Hz), 0.76 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.4, 172.7, 172.4, 138.3, 136.1, 129.6, 128.0, 117.3, 68.1, 55.2, 47.9, 41.6, 38.4, 35.7, 26.6, 24.5 and 21.6.

EXAMPLE 27 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-4-methyl-pentanoic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-leucine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (DMSO-d₆), 10.52 (1H, d, J=1.5 Hz), 8.82 (1H, d, J=5.1 Hz), 8.42 (1H, d, J=7.4 Hz), 5.67-5.51 (1H, m), 5.08-5.01 (1H, m), 4.96-4.87 (2H, m), (1H, m), 2.57-2.45 (1H, m), 2.27-2.04 (2H, m), 1.98-1.35 (14H, m) and 0.96-0.75 (13H, m). ¹³C-NMR; δ (DMSO-d₆), 174.3, 172.9, 170.0, 136.6, 117.1, 77.7, 51.2, 46.6, 40.2, 35.7, 32.9, 32.8, 25.8, 25.2, 25.1, 24.2, 23.8, 22.2 and 21.7.

EXAMPLE 28 3-Cyclohexyl-2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-propionic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-cyclohexylalanine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (DMSO-d₆), 10.50 (1H, d, J=1.4 Hz), 8.79 (1H, d, J=1.6 Hz), 8.39 (1H, d, J=7.7 Hz), 5.71-5.54 (1H, m), 5.11-5.03 (1H, m), 4.99-4.89 (2H, m), 4.37-4.26 (1H, m), 2.61-2.49 (1H, m), 2.30-2.08 (2H, m), 2.02-0.74 (25H, m), 0.87 (3H, d, J=6.4 Hz) and 0.81 (3H, d, J=6.4 Hz). ¹³C-NMR; δ (DMSO-d₆), 173.5, 172.3, 169.3, 135.9, 116.3, 77.0, 49.5, 46.0, 45.9, 40.3, 37.9, 35.0, 33.6, 33.2, 32.1, 31.2, 26.2, 26.1, 25.8, 25.2, 24.4, 23.5 and 21.5.

EXAMPLE 29 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 1-methyl-piperidin-4-yl Ester

2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 1-ethyl-propyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine 1-ethyl-propyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 8.65 (1H, d, J=8.5 Hz), 7.31-7.11 (5H, m), 5.50-5.33 (1H, m), 4.88-4.74 (4H, m), 3.27 (1H, dd, J=9.7, 4.6 Hz), 2.88 (1H, dd, J=13.9, 11.0 Hz), 2.46 (1H, dt, J=11.1, 3.1 Hz), 1.99 (1H, dt, J=11.4, 3.4 Hz), 1.89-1.76 (1H, m), 1.70-1.49 (6H, m), 1.33-1.24 (1H, m), 1.07-0.94 (1H, m) and 0.94-0.60 (12H, m). ¹³C-NMR; δ (methanol-d₄), 175.3, 172.0, 171.4, 137.4, 135.1, 129.2, 128.5, 127.0, 116.2, 78.5, 54.3, 46.9, 40.6, 37.5, 34.7, 26.7, 26.7, 25.6, 23.5 and 20.7.

EXAMPLE 31 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 1S-methyl-butyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine 1S-methyl-butyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 8.64 (1H, d, J=8.4 Hz), 7.29-7.12 (5H, m), 5.27 (1H, m), 4.89 (4H, m), 3.24 (1H, dd, J=13.9, 4.9 Hz), 2.88 (1H, dd, J=13.9, 10.8 Hz), 2.46 (1H, dt, J=11.3, 3.2 Hz), 1.99 (1H, dd, J=11.3, 3.4 Hz), 1.83 (1H, m), 1.64-1.41 (4H, bm), 1.33 (3H, m), 1.23 (3H, d, J=6.3 Hz), 1.09 (1H, m), 0.90 (6H, m) and 0.83 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.3, 172.6, 172.4, 138.4, 136.1, 130.3, 129.5, 128.0, 117.3, 73.3, 55.2, 47.9, 41.6, 39.1, 38.4, 35.7, 26.6, 24.6, 21.7, 20.3, 19.7 and 14.2.

EXAMPLE 32 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Cyclohexyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine cyclohexyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (DMSO-d₆), 10.39 (1H, s), 8.71 (1H, s), 8.42 (1H, d, J=8.0 Hz), 7.29-7.11 (5H, m), 5.39 (1H, ddt, J=17.0, 10.3, 6.6 Hz), 4.81 (1H, dd, J=10.3, 2.0 Hz), 4.73 (1H, dd, J=17.2, 2.0 Hz), 4.69-4.53 (2H, m), 3.09 (1H, dd, J=13.8, 4.8 Hz), 2.85 (1H, dd, J=13.8, 10.6 Hz), 2.47-2.34 (1H, m), 2.00-1.16 (15H, m), 0.93-0.78 (1H, m), 0.82 (3H, d, J=6.4 Hz) and 0.76 (3H, d, J=6.4 Hz). ¹³C-NMR; δ (DMSO-d₆), 173.7, 171.2, 169.6, 137.7, 136.2, 129.4, 128.4, 126.8, 116.2, 73.0, 53.7, 46.2, 45.9, 40.5, 36.9, 34.7, 31.3, 31.2, 25.3, 25.2, 24.6, 23.5 and 21.8.

EXAMPLE 33 2S-{2R-[1S-Hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3,3-dimethyl-butyric Acid Isopropyl Ester

The title compound was prepared using an analogous route to that described for example 17. 2-[1R-(1S-Isopropoxycarbonyl-2,2-dimethyl-propylcarbamoyl)-3-methyl-butyl]-acrylic acid was prepared from 3R-hydroxycarbonyl-2-benzyloxycarbonyl-5-methylhexanoic acid benzyl ester and L-tert-butyl glycine isopropyl ester using methods similar to those described in example 4. ¹H-NMR; δ (methanol-d₄), 7.44 (1H, m), 7.11 (1H, m), 6.96 (1H, m), 4.98 (1H, m), 4.23 (1H, s), 3.00 (1H, m), 2.79 (2H, m), 2.42 (1H, m), 1.53 (1H, m), 1,37 (1H, m), 1.24 (3H, s), 1.21 (3H, s), 1.11 (1H, m), 1.00 (9H, s), 0.88 (3H, d, J=6.4 Hz) and 0.81 (3H, d, J=6.6 Hz). ¹³C-NMR; δ (methanol-d₄), 176.3, 172.0, 171.5, 135.3, 131.2, 129.1, 70.3, 63.0, 48.4, 48.1, 42.0, 40.8, 35.2, 27.8, 27.2, 24.8, 22.5 and 22.2.

EXAMPLE 34 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid 1R-methyl-butyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine 1R-methyl-butyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.30-7.12 (5H, m), 5.57-5.34 (1H, m), 5.01-4.93 (1H, m), 4.84-4.70 (3H, m), 3.22 (1H, dd, J=13.9, 4.9 Hz), 2.88 (1H, dd, J=13.9, 10.9 Hz), 2.46 (1H, dt, J=11.1, 3.0 Hz), 1.99 (1H, dt, J=1.4, 3.3 Hz), 1.90-1.77 (1H, m), 1.68-1.21 (7H, m), 1.16 (3H, d, J=6.3 Hz), 1.12-0.89 (7H, m) and 0.83 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.3, 172.6, 172.4, 138.3, 137.9, 136.1, 130.3, 129.5, 128.0, 117.3, 73.2, 55.4, 47.9, 41.6, 39.2, 38.4, 35.7, 26.6, 24.6, 21.7, 20.2, 19.7 and 14.2.

EXAMPLE 35 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic Acid Tetrahydro-furan-3(R, S)-yl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylalanine tetrahydro-furan-3(R, S)-yl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.29-7.13 (5H, m), 5.51-5.29 (2H, m), 4.85-4.75 (3H, m), 3.91-3.66 (4H, m), 3.23 (1H, dd, J=14.0, 5.0 Hz), 2.96-2.86 (2H, m), 2.47 (1H, dt, J=11.7, 3.0 Hz), 2.28-2.10 (3H, m), 2.05-1.78 (3H, m), 1.55-1.44 (2H, m), 1.37-1.30 (1H, m), 1.03-0.92 (1H, m), 0.89 (3H, d, J=6.4 Hz) and 0.83 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.5, 172.7, 172.4, 138.2, 136.1, 130.3, 129.6, 128.1, 117.3, 77.3, 73.8, 67.9, 55.2, 47.9, 41.6, 38.2, 33.2, 26.7, 24.5 and 21.7.

EXAMPLE 36 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3,3-dimethyl-butyric Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-tert-butyl glycine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 5.71-5.57 (1H, m), 5.18-5.13 (1H, m), 5.03-4.95 (2H, m), 4.29 (1H, s), 2.76-2.66 (1H, m), 2.31-2.03 (3H, m), 1.90-1.38 (10H, m), 1.14-0.99 (2H, m), 1.06 (9H, s), 0.92 (3H, d, J=6.5 Hz) and 0.87 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 177.2, 172.8, 172.5, 136.4, 117.9, 79.7, 63.1, 42.2, 36.8, 35.2, 34.0, 33.8, 27.7, 25.1, 25.0, 24.9 and 22.3.

EXAMPLE 37 2S-[2R-(1S-Cyclopentyl-hydroxycarbamoyl-methyl)-4-methyl-pentanoylamino]-3-phenyl-propionic Acid Cyclopentyl Ester

The title compound was prepared using chemistry analogous to that described in WO 97/19053 involving an initial coupling between 2S-cyclopentyl-3R-isobutyl-succinic acid 1-benzyl ester and L-phenylalanine cyclopentyl ester. ¹H-NMR; δ (methanol-d₄), 8.51 (1H, d, J=8.1 Hz), 7.31-7.16 (5H, m), 5.13-5.04 (1H, m), 4.73-4.62 (3H, m), 3.01 (1H, dd, J=13.9, 6.4 Hz), 2.92 (1H, dd, J=13.9, 8.8 Hz), 2.78 (1H, dt, J=10.7, 3.8 Hz), 2.24-2.02 (3H, m), 1.90-1.21 (20H, m), 1.12-0.96 (1H, m) and 0.93-0.81 (1H, m). ¹³C-NMR; δ (methanol-d₄), 176.5, 173.2, 172.9, 144.0, 138.5, 130.6, 129.9, 128.4, 113.8, 79.8, 55.6, 51.5, 42.6, 41.3, 39.2, 33.9, 33.8, 32.3, 30.2, 26.5, 26.1, 25.0, 22.8 and 22.1.

EXAMPLE 38 2S-[2R-(1S-Hydroxy-hydroxycarbamoyl-methyl)-pent-4-ynoylamino]-3-phenylpropionic Acid Cyclopentyl Ester

(a) 2S-Hydroxy-3R-prop-2-ynyl-succinic Acid Diisopropyl Ester

A solution of S-malic acid diisopropyl ester (5.5 g, 25.2 mmol) in dry THF (20 ml) was added to a solution of freshly prepared lithium disopropylamide [from N,N-diisopropylamine (6.9 mL, 52. mmol) and 2.5 M n-butyllithium (21 mL, 52.5 mmol)] in dry THF (50 mL), whilst maintaining the temperature at −5° C. The reaction mixture was stirred at −5° C. for 75 minutes then cooled to −70° C. A solution of propargyl bromide (80% solution in toluene, 3.1 mL, 27.7 mmol) was added slowly, whilst maintaining the temperature at −70° C. The cooling bath was removed and the solution was stirred overnight before quenching with saturated aqueous ammonium chloride (50 mL). The aqueous layer was separated and extracted with ethyl acetate. The organic layers were combined and washed with 1M hydrochloric acid and brine and dried over anhydrous magnesium sulphate. The solution was filtered and concentrated in vacuo to give a brown oil which was purified by column chromatography (silica gel, 25% ethyl acetate in hexane) to provide the title compound as an orange oil (1.4 g, 22%; 9:1 mixture of diastereomers by NMR). ¹H-NMR; δ (CDCl₃, major diastereoisomer), 5.12 (1H, m), 5.04 (1H, m), 4.45 (1H, dd, J=5.8, 2.6 Hz), 3.17 (1H, d, J=5.8 Hz), 3.08 (1H, m), 2.67 (1H, m), 2.05 (1H, t, J=2.9 Hz), 1.29 (6H, d, J=6.1 Hz) and 1.19 (6H, d, J=6.2 Hz).

(b) 2S-Hydroxy-3R-prop-2-ynyl-succinic Acid

A solution of 2S-hydroxy-3R-prop-2-ynyl-succinic acid diisopropyl ester (2.47 g, 9.5 mmol) in 1M sodium hydroxide (32 mL, 3 mmol) was heated at reflux for 1 hour then cooled to room temperature. The solution was acidified to pH 2 with 1M hydrochloric acid and extracted with ethyl acetate. The combined organics were dried over magnesium sulphate, filtered and concentrated in vacuo to provide the title compound as a brown oil (0.94 g, 64%). ¹H-NMR; δ (methanol-d₄), 4.37 (1H, d, J=3.4 Hz), 3.01 (1H, m), 2.51 (2H, m), 2.21 (1H, t, J=2.5 Hz)

(c) 2R-(2,2-Dimethyl-5-oxo-[1,3]dioxolan-4S-yl)-pent-4-ynoic Acid

2S-Hydroxy-3R-prop-2-ynyl-succinic acid (0.94 g, 6.18 mmol) was dissolved in ethyl acetate (5 mL). Dimethoxypropane (10 mL) and p-toluenesulfonic acid (10 mg) were added and the solution heated at reflux for 2.5 hours. Solvents were removed in vacuo to provide the title compound as a dark brown gum (1.0 g 84%). ¹H-NMR; δ (CDCl₃), 4.80 (1H, d, J=2.4 Hz), 3.22 (1H, m), 2.86 (1H, ddd, J=17.2, 5.4, 2.6 Hz), 2.61 (12H, ddd, J=13.0, 10.3, 2.6 Hz), 2.10 (1H, t, J 2.8 Hz), 1.58 (3H, s) and 1.57 (3H, s).

(d) 2S-[2R-(1S-Hydroxy-hydroxycarbamoyl-methyl)-pent-4-ynoylamino]-3-phenylpropionic Acid Cyclopentyl Ester.

The title compound was prepared using an analogous route to that described in example 8. 2R-(2,2-Dimethyl-5-oxo-[1,3]dioxolan-4S-yl)-pent-4-ynoic acid pentafluorophenyl ester was prepared by treatment of 2R-(2,2-dimethyl-5-oxo-[1,3]dioxolan-4S-yl)-pent-4-ynoic acid with pentafluorophenol and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride in DCM. ¹H-NMR; δ (methanol-d₄), 7.31-7.18 (5H, m), 5.09-5.05 (1H, m), 4.64-4.58 (1H, m), 4.27 (1H, d, J=5.4 Hz), 3.06-2.92 (3H, m), 2.48 (2H, dd, J=7.6, 2.6 Hz), 2.32 (1H, t, J=2.6 Hz) and 1.84-1.47 (8H, bm). ¹³C-NMR; δ (methanol-d₄), 173.8, 172.6, 171.2, 137.8, 130.4, 129.5, 127.9, 79.7, 71.9, 55.4, 49.2, 38.8, 33.4, 33.3, 24.5 and 19.3.

EXAMPLE 39 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-yl-propionic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-3-pyridylalanine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (DMSO-d₆), 10.42 (1H, bs), 8.67 (1H, bs), 8.51-8.33 (3H, m), 7.74 (1H, d, J=7.9 Hz), 7.28 (1H, dd, J=7.7, 4.8 Hz), 5.37 (1H, ddt, J=17.0, 10.2 6.7 Hz), 5.09-5.02 (1H, m), 4.82 (1H, dd, J=10.2, 2.0 Hz), 4.73 (1H, dd, J=17.2, 2.0 Hz), 4.68-4.56 (1H, m), 3.12 (1H, dd, J=14.1, 4.8 Hz), 2.86 (1H, dd, J=14.0, 11.0 Hz), 2.41-2.30 (1H, m), 1.96-1.08 (13H, m), 0.92-0.74 (1H, m), 0.80 (3H, d, (J=6.4 Hz) and 0.76 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 173.7, 171.3, 169.5, 150.5, 147.9, 137.2, 133.4, 123.6, 116.4, 77.6, 53.0, 46.2, 45.9, 34.6, 33.9, 32.4, 32.3, 25.3, 24.6, 23.7 and 21.7.

EXAMPLE 40 3-tert-Butoxy-2S-(3S-hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-propionic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-tert-butoxyserine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (CDCl₃), 6.66 (1H, d, J=8.1 Hz), 5.73-5.63 (1H, m), 5.27-5.22 (1H, m), 5.10-4.99 (2H, m), 4.72-4.67 (1H, m), 3.80 (1H, dd, J=8.8, 3.0 Hz), 3.57 (1H, dd, J=8.8, 3.0 Hz), 2.65-2.57 (1H, m), 2.53-2.34 (2H, m), 2.22-2.17 (1H, m), 1.88-1.56 (11H, m), 1.19 (9H, s), 0.91(3H, d, J=6.5 Hz) and 0.87 (3H, d, J=6.5 Hz). 46.2, 39.7, 34.7, 32.6, 32.4, 27.2, 25.8, 23.8, 23.7, 23.6 and 21.3.

EXAMPLE 41 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-2-phenylethanoic Acid Cyclopentyl Ester

The title compound was prepared using an analogous route to that described for example 3 using L-phenylglycine cyclopentyl ester in place of L-phenylalanine isopropyl ester. ¹H-NMR; δ (methanol-d₄), 7.41-7.32 (5H, m), 5.70-5.49 (1H, m), 5.42 (1H, s), 5.21-5.15 (1H, m), 4.92-4.85 (2H, m), 2.69-2.61 (1H, m), 2.20-2.13 (2H, m), 1.95-1.51 (11H, m), 1.18-1.00 (1H, m), 0.95 (3H, d, J=6.5 Hz) and 0.89 (3H, d, J=6.5 Hz). ¹³C-NMR; δ (methanol-d₄), 176.3, 172.3, 171.5, 137.5, 135.9, 129.8, 129.6, 129.0, 117.4, 79.8, 58.7, 58.6, 48.3, 47.3, 41.5, 36.0, 33.3, 26.7, 24.5, 24.4 and 21.7.

EXAMPLE 42 2S-[5-(2-Chlorophenyl)-2R-(1S-hydroxy-hydroxycarbamoyl-methyl)-pent-4-ynoylamino]-3-phenylpropionic Acid Cyclopentyl Ester

(a) 5-(2-Chlorophenyl)-2R-(2,2-dimethyl)-5-oxo-[1,3]-dioxolan-4S-yl)-pent-4-ynoic Acid

2R-(2,2-Dimethyl-5-oxo-[1,3]dioxolan-4S-yl)-pent-4-ynoic acid (example 38, 3 g, 15.6 mmol) and 1-chloro-2-iodobenzene (1.59 mL, 13.0 mmol) were dissolved in a mixture of diisopropylamine (5.2 mL) and DCM (20 mL) in a 35 mL pressure tube. Dichlorobis(triphenylphosphine)palladium(II) (379 mg, 4.6 mol %) and copper (I) iodide (89 mg, 4.0 mol %) were added and the tube heated at room temperature for 4 hours. The reaction mixture was partitioned between DCM and 1M hydrochloric acid. The product was extracted with saturated aqueous sodium hydrogen carbonate. The basic extracts were combined, acidified to pH2 with 1M hydrochloric acid then extracted with dichloromethane. Combined organics were dried (magnesium sulphate), filtered and solvents removed in vacuo to provide the title compound as an orange solid (3.2 g, 81%). ¹H-NMR; δ (CDCl₃), 7.46-7.37 (2H, m), 7.28-7.17 (2H, m), 5.00 (1H, d, J=2.8 Hz), 3.39-3.32 (1H, m), 3.16 (1H, dd, J=17.3, 5.2 Hz), 2.92 (1H, dd, J=17.8, 10.7 Hz), 1.60 (3H, s) and 1.58 (3H, s).

(b) 2S-[5-(2-Chlorophenyl)-2R-(1S-hydroxy-hydroxycarbamoyl-methyl)-pent-4-ynoylamino]-3-phenylpropionic Acid Cyclopentyl Ester.

The title compound was prepared using an analogous route to that described for example 8 using 5-(2-chlorophenyl)-2R-(2,2-dimethyl)-5-oxo-[1,3]-dioxolan-4S-yl)-pent-4-ynoic acid pentafluorophenyl ester in place of 2R-(2,2-dimethyl-5-oxo-[1,3-dioxolan-4S-yl)-4-methyl-pentanoic acid pentafluorophenyl ester. The pentafluorophenyl ester was prepared by treatment of 5-(2-chlorophenyl)-2R-(2,2-dimethyl)-5-oxo-[1,3]-dioxolan-4S-yl)-pent-4-ynoic acid with pentafluorophenol and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride in DCM. ¹H-NMR; δ (methanol-d₄), 8.30 (1H, d, J=6.8 Hz), 7.48-7.23 (9H, bm), 5.00 (1H, m), 4.67-4.65 (1H, m), 4.35 (1H, d, J=4.6 Hz), 3.10-2.97 (3H, m), 2.78 (2H, d, J=7.1 Hz) and 1.50 (8H, bm). ¹³C-NMR; δ (methanol-d₄), 173.8, 172.5, 171.3, 137.8, 136.8, 134.7, 130.5, 130.3, 130.2, 129.5, 127.9, 127.7, 92.9, 80.3, 79.6, 72.2, 55.5, 39.0, 33.5, 33.3, 24.6, 24.5 and 20.2.

EXAMPLE 43 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-6-phenyl-hex-5-enoylamino)-3-phenyl-propionic Acid Cyclopentyl Ester

(a) 2S-[1R-(1S-Cyclopentyloxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-5-phenyl-pent-4-enoic Acid.

A solution of 2S-[1R-(1S-cyclopentyloxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-pent-4-enoic acid.(previously prepared for example 20) (400 mg, 0.93 mmol), palladium acetate (10.6 mg, 0.10 mmol), tri-ortho-tolyl phosphine (28 mg, 0.6 mmol), iodobenzene (208 μL, 1.86 mmol) and triethylamine (250 μL, 1.86 mmol)) in acetonitrile was heated at 75° C. for 1 hour. The cooled reaction mixture was partitioned between ethyl acetate and 1.0M hydrochloric acid. The organic layer was washed with water and brine, dried over anhydrous magnesium sulphate, filtered and evaporated. Purification by chromatography on silica gel gave the product as a white powder (99 mg, 0.2 mmol, 21%). ¹H-NMR; δ (CDCl₃), 7.36-7.18 (8H, m), 7.13-7.07 (2H, m), 6.37 (1H, d, J=15.7 Hz), 6.17 (1H, d, J=8.1 Hz), 6.08-5.69 (1H, m), 5.23-5.17 (1H, m), 4.91-4.80 (1H, m), 3.18 (1H, dd, J=14.0, 5.9 Hz), 3.01 (1H, dd, J=14.0, 7.0 Hz), 2.63-2.50 (2H, m), 2.45-2.37 (1H, m), 2.23-2.07 (1H, m), 1.92-1.44 (10H, m), 1.27-1.24 (1H, m), 0.86 (3H, d, J=6.5 Hz), 0.85 (3H, d, J=6.4 Hz).

(b) 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-6-phenyl-hex-5-enoylamino)-3-phenyl-propionic Acid Cyclopentyl Ester.

The title compound was prepared from 2S-[1R-(1S-cyclopentyloxycarbonyl-2-phenyl-ethylcarbamoyl)-3-methyl-butyl]-5-phenyl-pent-4-enoic acid using chemistry previously described eg example 3c. ¹H-NMR; δ (methanol-d₄), 8.63-8.49 (1H, m), 7.24-6.96 (10H, m), 6.17-6.02 (1h, m), 5.90-5.69 (1H, m), 5.13-5.04 (1H, m), 4.75-4.68 (1H, m), 3.13 (1H, dd, J=13.9, 5.4 Hz), 2.81 (1H, dd, J=13.9, 10.5 Hz), 2.53-2.29 (2H, m), 2.01-1.34 (12H, m), 1.02-0.90 (1H, m), 0.83(3H, d, J=6.4 Hz), 0.75 (3H, d, J=6.6 Hz).

BIOLOGICAL EXAMPLE

The compounds of examples 1-5 were tested in the following cell proliferation assay, to determine their respective capacities to inhibit proliferation of the cell types in question.

Two human cell lines namely a histiocytic lymphoma (U937) and a melanoma (RPMI-7951) were seeded into 30 mm² tissue culture wells, in the appropriate culture medium supplemented with 10% fetal calf serum at a density of 250 cells/mm². Six hours later the test compounds were added in the same culture medium to the cells to give a final concentration of 6 μM. Control wells contained cells supplemented with the same culture medium containing the equivalent amount of drug vehicle, which in this case was DMSO at a final concentration of 0.08%. After 72 hours in culture the cells were pulsed for 3 hours with [methyl-³[H] Thymidine] (2 μCi/ml) and the harvested onto filter mats and DNA associated radioactivity counted. Results percentage of control ³[H] Thymidine incorporation (n=6±1 stdv).

The results obtained are set out in the following Table:

Activities Example U937 RPMI 1 7 40 2 7 37 3 2.5 27 4 93 not tested 5 19 82

Further examples were tested in the U937 assay described above at 6 μM and the results, expressed as percentage of control ³[H] Thymidine incorporation (n=6±1 stdv), are set out in the following Table:

Example U937 6 18  7 0 8 1 9 8 10  1 11  0 12  10  13  4 14  33  15  19  16  2 17  0 18  54  19  Not tested 20  0 21  1 22  51  23  36  24  50  25  34  26  0 27  0 28  0 29  49  30  6 31  7 32  0 33  Not tested 34  3 35  14  36  51  37  0 38  37  39  26  40  0 41  0 42  0 43  Not tested

For comparison, the activity in the above U9357 assay of the known cytotoxic agent 5-fluorouracil (5-FU) at 6 μM was found to be 50% of that observed with the vehicle alone. (n=6±1 stdv), are set out in the following Table: 

What is claimed is:
 1. A method for inhibiting proliferation of tumor cells in a mammal, comprising administering to the mammal suffering such cell proliferation an amount of a compound of general formula (I), or a pharmaceutically acceptable salt, hydrate or solvate thereof, sufficient to inhibit such proliferation:

wherein R is hydrogen or (C₁-C₆) alkyl; R₁ is hydrogen; (C₁-C₆) alkyl; (C₂-C₆) alkenyl; phenyl or substituted phenyl; phenyl (C₁-C₆) alkyl or substituted phenyl (C₁-C₆) alkyl; phenyl (C₂-C₆) alkenyl or substituted phenyl (C₂-C₆) alkenyl heterocyclyl or substituted heterocyclyl; heterocyclyl (C₁-C₆) alkyl or substituted heterocyclyl (C₁-C₆) alkyl; a group BSOA_(n) wherein n is 0, 1 or 2 and B is hydrogen or a (C₁-C₆) alkyl, phenyl, substituted phenyl, heterocyclyl substituted heterocyclyl, (C₁-C₆) acyl, phenacyl or substituted phenacyl group, and A represents (C₁-C₆) alkylene; hydroxy or (C₁-C₆) alkoxy; amino, protected amino, acylamino, (C₁-C₆) alkylamino or di-(C₁-C₆) alkylamino; mercapto, or (C₁-C₆) alkylthio; amino (C₁-C₆) alkyl, (C₁-C₆) alkylamino (C₁-C₆) alkyl, di(C₁-C₆) alkylamino (C₁-C₆) alkyl, hydroxy (C₁-C₆) alkyl, mercapto (C₁-C₆) alkyl or carboxy (C₁-C₆) alkyl wherein the amino-, hydroxy-, mercapto- or carboxyl-group are optionally protected or the carboxyl-group amidated; lower alkyl substituted by carbamoyl, mono(lower alkyl)carbamoyl, di(lower alkyl)carbamoyl, di(lower alkyl)amino, or carboxy-lower alkanoylamino; or a cycloalkyl, cycloalkenyl or non-aromatic heterocyclic ring containing up to 3 heteroatoms, any of which may be (i) substituted by one or more substituents selected from C₁-C₆ alkyl, C₂-C₆ alkenyl, halo, cyano (—CN), —CO₂H, —CO₂R, —CONH₂, —CONHR, —CON(R)₂, —OH, —OR, oxo-, —SH, —SR, —NHCOR, and —NHCO₂R wherein R is C₁-C₆ alkyl or benzyl and/or (ii) fused to a cycloalkyl or heterocyclic ring; R₂ is a C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, phenyl (C₁-C₆ alkyl)-, heteroaryl (C₁-C₆ alkyl)-, phenyl (C₂-C₆ alkenyl)-, heteroaryl (C₂-C₆ alkenyl)-, phenyl (C₂-C₆ alkynyl)-, heteroaryl (C₂-C₆ alkynyl)-, cycloalkyl (C₁-C₆ alkyl)-, cycloalkyl (C₂-C₆ alkenyl)-, cycloalkyl (C₂-C₆ alkynyl)-, cycloalkenyl (C₁-C₆ alkyl)-, cycloalkenyl(C₂-C₆ alkenyl)-, cycloalkenyl(C₂-C₆ alkynyl)-, phenyl (C₁-C₆ alkyl)O(C₁-C₆ alkyl)-, or heteroaryl(C₁-C₆ alkyl)O(C₁-C₆ alkyl)- group, any one of which may be substituted by C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, cyano (—CN), phenyl, or phenyl substituted by C₁-C₆ alkyl, C₁-C₆ alkoxy, halo, or cyano (—CN); R₃ is the side chain of a natural or non-natural α amino acid in which any functional groups may be protected; and R₄ is an ester or thioester group.
 2. A method according to claim 1 wherein the stereochemical configuration of the carbon atom carrying the groups R₃ and R₄ is S.
 3. A method according to claim 1 or claim 2 wherein R, is: hydrogen, methyl, ethyl, n-propyl, n-butyl, isobutyl, hydroxyl, methoxy, allyl, phenylpropyl, phenylprop-2-enyl, thienylsulphanylmethyl, thienylsulphinylmethyl, or thienylisulphonylmethyl; or C₁-C₄ alkyl, substituted by a moiety selected from the group consisting of phthalimido, 1,2-dimethyl-3,5-dioxo-1,2,4-triazolidin-4-yl, 3-methyl-2,5-dioxo-1-imidazolidinyl, 3,4,4-trimethyl-2,5-dioxo-1-imidazolidinyl, 2-methyl-3,5-dioxo-1,2,4-oxadiazol-4-yl, 3-methyl-2,4,5-trioxo-1-imidazolidinyl, 2,5-dioxo-3-phenyl-1-imidazolidinyl, 2-oxo-1-pyrrolidinyl, 2,5-dioxo-1-pyrrolidinyl or 2,₆-dioxopiperidinyl, 5,5-dimethyl-2,4-dioxo-3-oxazolidinyl, hexahydro-1,3-dioxopyrazolo[1,2,a][1,2,4]-triazol-2-yl, or a naphthylimido 1,3-dihydro-1-oxo-2H-benz[f]lisoindol-2-yl, 1,3-dihydro-1,3-dioxo-2H-pyrrolo[3,4-b]quinolin-2-yl, or 2,3-dihydro-1,3-dioxo-¹H-benz[d,e]isoquinolin-2-yl group; orcyclohexyl, cyclooctyl, cycloheptyl, cyclopentyl, cyclobutyl, cyclopropyl, tetrahydropyranyl and morpholinyl.
 4. A method according to claim 1 or claim 2 wherein R₁is n-propyl, allyl, methoxy or thienylsulfanyl-methyl.
 5. A method according to claim 1 or claim 2 wherein R₂ is: C₁-C₁₂ alkyl, C₃-C₆ alkenyl or C₃-C₆ alkynyl; phenyl(C₁-C₆ alkyl)-, phenyl(C₃-C₆ alkenyl)- or phenyl(C₃-C₆ alkynyl)- optionally substituted in the phenyl ring; heteroaryl(C₁-C₆ alkyl)-, heteroaryl(C₃-C₆ alkenyl)- or heteroaryl(C₃-C₆ alkynyl)- optionally substituted in the heteroaryl ring; 4-phenylphenyl(C₁-C₆ alkyl)-, 4-phenylphenyl(C₃-C₆ alkenyl)-, 4-phenylphenyl(C₃-C₆ alkynyl)-, 4-heteroarylphenyl(C₁-C₆ alkyl)-, 4-heteroarylphenyl(C₃-C₆ alkenyl)-, 4-heteroarylphenyl(C₃-C₆ alkynyl)-, optionally substituted in the terminal phenyl or heteroaryl ring; or phenoxy(C₁-C₆ alkyl)- or heteroaryloxy(C₁-C₆ alkyl)- optionally substituted in the phenyl or heteroaryl ring.
 6. A method according to claim 1 or claim 2 wherein R₂ is: methyl, ethyl, n- or iso-propyl, n-, iso- or tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-nonyl, n-decyl, prop-2-yn-1-yl, 3-phenylprop-2-yn-1-yl, 3-(2-chlorophenyl)prop-2-yn-1-yl, phenylpropyl, 4-chlorophenylpropyl, 4-methylphenylpropyl, 4-methoxyphenylpropyl, phenoxybutyl, 3-(4-pyridylphenyl)propyl-, 3-(4-(4-pyridyl)phenyl)prop-2-yn-1-yl, 3-(4-phenylphenyl)propyl-, 3-(4-phenyl)phenyl)prop-2-yn-1-yl or 3-[(4-chlorophenyl)phenyl]propyl-.
 7. A method according to claim 1 or claim 2 wherein R₂ is isobutyl, n-hexyl, or 3-(2-chlorophenyl)prop-2-yn-1-yl.
 8. A method according to claim 1 or claim 2 wherein R₃ is C₁-C₆ alkyl, phenyl, 2-, 3-, or 4-hydroxyphenyl, 2-, 3-, or 4-methoxyphenyl, 2-, 3-, or 4-pyridylmethyl, benzyl, 2-, 3-, or 4-hydroxybenzyl, 2-, 3-, or 4-benzyloxybenzyl, 2-, 3-, or 4-C₁-C₆ alkoxybenzyl, or benzyloxy(C₁-C₆alkyl)-.
 9. A method according to claim 1 or claim 2 where in R₃ is the characterising group of a natural α amino acid, in which any functional group may be protected, any amino group may be acylated and any carboxyl group present may be amidated.
 10. A method according to claim 1 or claim 2 wherein R₃ is a group -[Alk]_(n)R₆ where Alk is a (C₁-C₆)alkyl or (C₂-C₆)alkenyl group optionally interrupted by one or more —O—, or —S— atoms or —N(R₇)— groups, wherein R₆ is an optionally substituted cycloalkyl or cycloalkenyl group, R₇ is a hydrogen atom or a (C₁-C₆)alkyl group, and n is 0 to
 1. 11. A method according to claim 1 or claim 2 wherein R₃ is a benzyl group substituted in the phenyl ring by a group of formula —OCH₂COR₈ where R₈ is hydroxyl, amino, (C₁-C₆)alkoxy, phenyl(C₁-C₆)alkoxy, (C₁-C₆)alkylamino, di((C₁-C₆)alkyl)amino, phenyl(C₁-C₆)alkylamino, the residue of an amino acid or acid halide, ester or amide derivative thereof, said residue being linked via an amide bond, said amino acid being selected from glycine, α or β alanine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, serine, threonine, cysteine, methionine, asparagine, glutamine, lysine, histidine, arginine, glutamic acid, and aspartic acid.
 12. A method according to claim 1 or claim 2 wherein R₃ is a heterocyclic(C₁-C₆)alkyl group, either being unsubstituted or mono- or di-substituted in the heterocyclic ring with halo, nitro, carboxy, (C₁-C₆)alkoxy, cyano, (C₁-C₆)alkanoyl, trifluoromethyl (C₁-C₆)alkyl, hydroxy, formyl, amino, (C₁-C₆)alkylamino, di-(C₁-C₆)alkylamino, mercapto, (C₁-C₆)alkylthio, hydroxy(C₁-C₆)alkyl, mercapto(C₁-C₆)alkyl or (C₁-C₆)alkylphenylmethyl.
 13. A method according to claim 1 or claim 2 wherein R₃ is a group —CR_(a)R_(b)R_(c) in which: each of R_(a), R_(b) and R_(c) is independently hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, (C₃-C₈)cycloalkyl; or R_(c) is hydrogen and R_(a) and R_(b) are independently phenyl or heteroaryl; or R_(c) is hydrogen, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or (C₃-C₈)cycloalkyl, and R_(a) and R_(b) together with the carbon atom to which they are attached form a 3 to 8 membered cycloalkyl or a 5- or 6-membered heterocyclic ring; or R_(a), R_(b) and R_(c) together with the carbon atom to which they are attached form a tricyclic ring; or R_(a) and R_(b) are each independently (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, phenyl(C₁-C₆)alkyl, or a group as defined for R_(c) below other than hydrogen, or R_(a) and R_(b) together with the carbon atom to which they are attached form a cycloalkyl or heterocyclic ring, and R_(c) is hydrogen, —OH, —SH, halogen, —CN, —CO₂H, (C₁-C₄)perfluoroalkyl, —CH₂OH, —CO₂(C₁-C₆)alkyl, —O(C₁-C₆)alkyl, —O(C₂-C₆)alkenyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —S(C₂-C₆)alkenyl, —SO(C₂-C₆)alkenyl, —SO₂(C₂-C₆)alkenyl or a group —Q—W wherein Q represents a bond or —O—, —S—, —SO— or —SO₂— and W represents a phenyl, phenylalkyl, (C₃-C₈)cycloalkyl, (C₃-C₈)cycloalkylalkyl, (C₄-C₈)cycloalkenyl, (C₄-C₆)cycloalkenylalkyl, heteroaryl or heteroarylalkyl group, which group W may be substituted by one or more substituents independently selected from, hydroxyl, halogen, —CN, —CO₂H, —CO₂(C₁-C₆)alkyl, —CONH₂, —CONH(C₁-C₆)alkyl, —CONH(C₁-C₆alkyl)₂, —CHO, —CH₂OH, (C₁-C₄)perfluoroalkyl, —O(C₁-C₆)alkyl, —S(C₁-C₆)alkyl, —SO(C₁-C₆)alkyl, —SO₂(C₁-C₆)alkyl, —NO₂, —NH₂, —NH(C₁-C₆)alkyl, —N((C₁-C₆)alkyl₂, —NHCO(C₁-C₆)alkyl, (C₁-C₆)alkyl, (C₂-C₆)alkenyl, (C₂-C₆)alkynyl, (C₃-C₈)cycloalkyl, (C₄-C₈)cycloalkenyl, phenyl or benzyl.
 14. A method according to claim 1 or claim 2 wherein R₃ is phenyl, benzyl, tert-butoxymethyl or iso-butyl.
 15. A method according to claim 1 or claim 2 wherein R₄ is a group of formula —(C═O)OR₉, —(C═O)SR₉, —(C═S)SR₉, and —(C═S)OR₉ wherein R₉ is (C₁-C₆)alkyl, (C₂-C₆)alkenyl, cycloalkyl, cycloalkyl(C₁-C₆)alkyl-, phenyl, heterocyclyl, phenyl(C₁-C₆)alkyl-, heterocyclyl(C₁-C₆)alkyl-, (C₁-C₆)alkoxy(C₁-C₆)alkyl-, or (C₁-C₆)alkoxy(C₁-C₆)alkoxy(C₁-C₆)alkyl-, any of which may be substituted on a ring or non-ring carbon atom or on a ring heteroatom, if present.
 16. A method according to claim 1 or claim 2 wherein R₄ is a group of formula —(C═O)OR₉ wherein R₉ is methyl, ethyl, n-or iso-propyl, n-, sec- or tert-butyl, 1-ethyl-prop-1-yl, 1-methyl-prop-1-yl, 1-methyl-but-1-yl, cyclopentyl, cyclohexyl, allyl, phenyl, benzyl, 2-, 3- and 4-pyridylmethyl, N-methylpiperidin-4-yl, 1-methylcyclopent-1yl, adamantyl, tetrahydrofuran-3-yl or methoxyethyl.
 17. A method according to claim 1 or claim 2 wherein R₄ is a group of formula —(C═O)OR₉ wherein R₉ is benzyl, cyclopentyl, isopropyl or tert-butyl.
 18. A method according to claim 1 or claim 2 wherein R is hydrogen or methyl.
 19. A method according to claim 1 or claim 2 wherein R₁ is n-propyl, allyl, methoxy or thienylsulfanyl-methyl, R₂ is isobutyl, n-hexyl, or 3-(2-chlorophenyl)prop-2-yn-1-yl, R₃ is phenyl, benzyl, tert-butoxymethyl or iso-butyl, R₄ is a group of formula —(C═O)OR₉ wherein R₉ is benzyl, cyclopentyl, isopropyl or tert-butyl and R is hydrogen or methyl.
 20. A method according to claim 1 wherein the tumor cell proliferation is that associated with a disorder selected from the group consisting of lymphoma, leukemia, myeloma, adenocarcinoma, carcinoma, mesothelioma, teratocarcinoma, choriocarcinoma, small cell carcinoma, large cell carcinoma, melanoma, retinoblastoma, fibrosarcoma, leiomyosarcoma, glioblastoma and endothelioma.
 21. A method as claimed in claim 2 or claim 20 wherein the compound is selected from the group consisting of 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid cyclopentyl ester, 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-3-phenylpropionic acid benzyl ester, 2S-{2R-[1S-Hydroxycarbamoyl-2-(thiophen-2-ylsulphanyl)-ethyl]-4-methyl-pentanoylamino}-3-phenyl-propionic acid isopropyl ester, 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-4-methyl-pentanoic acid cyclopentyl ester, and pharmaceutically acceptable salts, hydrates and esters thereof.
 22. The method according to claim 2, wherein the compound used in the treatment is 2S-(3S-Hydroxycarbamoyl-2R-isobutyl-hex-5-enoylamino)-2-phenylethanoic acid cyclopentyl ester.
 23. A method according to claim 3 wherein the C₁-C₄ alkyl substituent is methyl, ethyl, n-propyl or n-butyl.
 24. A method according to claim 13 wherein the heteroaryl moiety is pyridyl.
 25. A method for inhibiting proliferation of tumor cells in a mammal, comprising administering to the mammal suffering such cell proliferation an amount of a compound of general formula (I), or a pharmaceutically acceptable salt, hydrate or solvate thereof, sufficient to inhibit such proliferation:

wherein R₁ is n-propyl, allyl, methoxy, ethoxy or hydroxy, R₂ is isobutyl, R₃ is phenyl, R₄ is a group of formula —(C═O)OR₉ wherein R₉ is cyclopentyl or cyclohexyl, R is hydrogen and the stereochemical configuration of the carbon atom carrying the groups R₃ and R₄ is S.
 26. The method according to claim 3 wherein R is C₁-C₄-alkyl substituted with naphthylimido, wherein said naphthylimido is 1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl. 